mounted on a barrier, insulates the conductor from the barrier for the
purpose of conducting current from one side of the barrier to the
other.
    Cable. A conductor with insulation, or a stranded conductor with or
without insulation and other coverings (single-conductor cable), or a
combination of conductors insulated from one another (multiple-
conductor cable).
    Cable sheath. A conductive protective covering applied to cables.

    Note to the definition of ``cable sheath'': A cable sheath may
consist of multiple layers one or more of which is conductive.

    Circuit. A conductor or system of conductors through which an
electric current is intended to flow.
    Clearance (between objects). The clear distance between two objects
measured surface to surface.
    Clearance (for work). Authorization to perform specified work or
permission to enter a restricted area.
    Communication lines. (See Lines; (1) Communication lines.)
    Conductor. A material, usually in the form of a wire, cable, or bus
bar, used for carrying an electric current.
    Contract employer. An employer, other than a host employer, that
performs work covered by Subpart V of this part under contract.
    Covered conductor. A conductor covered with a dielectric having no
rated insulating strength or having a

rated insulating strength less than the voltage of the circuit in which
the conductor is used.
    Current-carrying part. A conducting part intended to be connected
in an electric circuit to a source of voltage. Non-current-carrying
parts are those not intended to be so connected.
    Deenergized. Free from any electrical connection to a source of
potential difference and from electric charge; not having a potential
that is different from the potential of the earth.

    Note to the definition of ``deenergized'': The term applies only
to current-carrying parts, which are sometimes energized (alive).

    Designated employee (designated person). An employee (or person)
who is assigned by the employer to perform specific duties under the
terms of this subpart and who has sufficient knowledge of the
construction and operation of the equipment, and the hazards involved,
to perform his or her duties safely.
    Electric line truck. A truck used to transport personnel, tools,
and material for electric supply line work.
    Electric supply equipment. Equipment that produces, modifies,
regulates, controls, or safeguards a supply of electric energy.
    Electric supply lines. (See ``Lines; (2) Electric supply lines.'')
    Electric utility. An organization responsible for the installation,
operation, or maintenance of an electric supply system.
    Enclosed space. A working space, such as a manhole, vault, tunnel,
or shaft, that has a limited means of egress or entry, that is designed
for periodic employee entry under normal operating conditions, and
that, under normal conditions, does not contain a hazardous atmosphere,
but may contain a hazardous atmosphere under abnormal conditions.
    Energized (alive, live). Electrically connected to a source of
potential difference, or electrically charged so as to have a potential
significantly different from that of earth in the vicinity.
    Energy source. Any electrical, mechanical, hydraulic, pneumatic,
chemical, nuclear, thermal, or other energy source that could cause
injury to employees.
    Entry (as used in Sec.  1926.953). The action by which a person
passes through an opening into an enclosed space. Entry includes
ensuing work activities in that space and is considered to have
occurred as soon as any part of the entrant's body breaks the plane of
an opening into the space.
    Equipment (electric). A general term including material, fittings,
devices, appliances, fixtures, apparatus, and the like used as part of
or in connection with an electrical installation.
    Exposed, Exposed to contact (as applied to energized parts). Not
isolated or guarded.
    Fall restraint system. A fall protection system that prevents the
user from falling any distance.
    First-aid training. Training in the initial care, including
cardiopulmonary resuscitation (which includes chest compressions,
rescue breathing, and, as appropriate, other heart and lung
resuscitation techniques), performed by a person who is not a medical
practitioner, of a sick or injured person until definitive medical
treatment can be administered.
    Ground. A conducting connection, whether planned or unplanned,
between an electric circuit or equipment and the earth, or to some
conducting body that serves in place of the earth.
    Grounded. Connected to earth or to some conducting body that serves
in place of the earth.
    Guarded. Covered, fenced, enclosed, or otherwise protected, by
means of suitable covers or casings, barrier rails or screens, mats, or
platforms, designed to minimize the possibility, under normal
conditions, of dangerous approach or inadvertent contact by persons or
objects.

    Note to the definition of ``guarded'': Wires that are insulated,
but not otherwise protected, are not guarded.

    Hazardous atmosphere. An atmosphere that may expose employees to
the risk of death, incapacitation, impairment of ability to self-rescue
(that is, escape unaided from an enclosed space), injury, or acute
illness from one or more of the following causes:
    (1) Flammable gas, vapor, or mist in excess of 10 percent of its
lower flammable limit (LFL);
    (2) Airborne combustible dust at a concentration that meets or
exceeds its LFL;

    Note to the definition of ``hazardous atmosphere'' (2): This
concentration may be approximated as a condition in which the dust
obscures vision at a distance of 1.52 meters (5 feet) or less.

    (3) Atmospheric oxygen concentration below 19.5 percent or above
23.5 percent;
    (4) Atmospheric concentration of any substance for which a dose or
a permissible exposure limit is published in Subpart D, Occupational
Health and Environmental Controls, or in Subpart Z, Toxic and Hazardous
Substances, of this part and which could result in employee exposure in
excess of its dose or permissible exposure limit;

    Note to the definition of ``hazardous atmosphere'' (4): An
atmospheric concentration of any substance that is not capable of
causing death, incapacitation, impairment of ability to self-rescue,
injury, or acute illness due to its health effects is not covered by
this provision.

    (5) Any other atmospheric condition that is immediately dangerous
to life or health.

    Note to the definition of ``hazardous atmosphere'' (5): For air
contaminants for which the Occupational Safety and Health
Administration has not determined a dose or permissible exposure
limit, other sources of information, such as Material Safety Data
Sheets that comply with the Hazard Communication Standard, Sec.
1926.1200, published information, and internal documents can provide
guidance in establishing acceptable atmospheric conditions.

    High-power tests. Tests in which the employer uses fault currents,
load currents, magnetizing currents, and line-dropping currents to test
equipment, either at the equipment's rated voltage or at lower
voltages.
    High-voltage tests. Tests in which the employer uses voltages of
approximately 1,000 volts as a practical minimum and in which the
voltage source has sufficient energy to cause injury.
    High wind. A wind of such velocity that one or more of the
following hazards would be present:
    (1) The wind could blow an employee from an elevated location,
    (2) The wind could cause an employee or equipment handling material
to lose control of the material, or
    (3) The wind would expose an employee to other hazards not
controlled by the standard involved.

    Note to the definition of ``high wind'': The Occupational Safety
and Health Administration normally considers winds exceeding 64.4
kilometers per hour (40 miles per hour), or 48.3 kilometers per hour
(30 miles per hour) if the work involves material handling, as
meeting this criteria, unless the employer takes precautions to
protect employees from the hazardous effects of the wind.

    Host employer. An employer that operates, or that controls the
operating procedures for, an electric power generation, transmission,
or distribution installation on which a contract employer is performing
work covered by Subpart V of this part.

    Note to the definition of ``host employer'': The Occupational
Safety and Health Administration will treat the electric utility or
the owner of the installation as the host employer if it operates or
controls operating procedures for the installation. If the electric
utility or installation owner neither operates

nor controls operating procedures for the installation, the
Occupational Safety and Health Administration will treat the
employer that the utility or owner has contracted with to operate or
control the operating procedures for the installation as the host
employer. In no case will there be more than one host employer.

    Immediately dangerous to life or health (IDLH). Any condition that
poses an immediate or delayed threat to life or that would cause
irreversible adverse health effects or that would interfere with an
individual's ability to escape unaided from a permit space.

    Note to the definition of ``immediately dangerous to life or
health'': Some materials--hydrogen fluoride gas and cadmium vapor,
for example--may produce immediate transient effects that, even if
severe, may pass without medical attention, but are followed by
sudden, possibly fatal collapse 12-72 hours after exposure. The
victim ``feels normal'' from recovery from transient effects until
collapse. Such materials in hazardous quantities are considered to
be ``immediately'' dangerous to life or health.

    Insulated. Separated from other conducting surfaces by a dielectric
(including air space) offering a high resistance to the passage of
current.

    Note to the definition of ``insulated'': When any object is said
to be insulated, it is understood to be insulated for the conditions
to which it normally is subjected. Otherwise, it is, for the purpose
of this subpart, uninsulated.

    Insulation (cable). Material relied upon to insulate the conductor
from other conductors or conducting parts or from ground.
    Isolated. Not readily accessible to persons unless special means
for access are used.
    Line-clearance tree trimming. The pruning, trimming, repairing,
maintaining, removing, or clearing of trees, or the cutting of brush,
that is within the following distance of electric supply lines and
equipment:
    (1) For voltages to ground of 50 kilovolts or less--3.05 meters (10
feet);
    (2) For voltages to ground of more than 50 kilovolts--3.05 meters
(10 feet) plus 0.10 meters (4 inches) for every 10 kilovolts over 50
kilovolts.
    Lines. (1) Communication lines. The conductors and their supporting
or containing structures which are used for public or private signal or
communication service, and which operate at potentials not exceeding
400 volts to ground or 750 volts between any two points of the circuit,
and the transmitted power of which does not exceed 150 watts. If the
lines are operating at less than 150 volts, no limit is placed on the
transmitted power of the system. Under certain conditions,
communication cables may include communication circuits exceeding these
limitations where such circuits are also used to supply power solely to
communication equipment.

    Note to the definition of ``communication lines'': Telephone,
telegraph, railroad signal, data, clock, fire, police alarm, cable
television, and other systems conforming to this definition are
included. Lines used for signaling purposes, but not included under
this definition, are considered as electric supply lines of the same
voltage.

    (2) Electric supply lines. Conductors used to transmit electric
energy and their necessary supporting or containing structures. Signal
lines of more than 400 volts are always supply lines within this
section, and those of less than 400 volts are considered as supply
lines, if so run and operated throughout.
    Manhole. A subsurface enclosure that personnel may enter and that
is used for installing, operating, and maintaining submersible
equipment or cable.
    Minimum approach distance. The closest distance an employee may
approach an energized or a grounded object.

    Note to the definition of ``minimum approach distance'':
Paragraph (c)(1)(i) of Sec.  1926.960 requires employers to
establish minimum approach distances.

    Personal fall arrest system. A system used to arrest an employee in
a fall from a working level.
    Qualified employee (qualified person). An employee (person)
knowledgeable in the construction and operation of the electric power
generation, transmission, and distribution equipment involved, along
with the associated hazards.

    Note 1 to the definition of ``qualified employee (qualified
person)'': An employee must have the training required by Sec.
1926.950(b)(2) to be a qualified employee.

    Note 2 to the definition of ``qualified employee (qualified
person)'': Except under Sec.  1926.954(b)(3)(iii), an employee who
is undergoing on-the-job training and who has demonstrated, in the
course of such training, an ability to perform duties safely at his
or her level of training and who is under the direct supervision of
a qualified person is a qualified person for the performance of
those duties.

    Statistical sparkover voltage. A transient overvoltage level that
produces a 97.72-percent probability of sparkover (that is, two
standard deviations above the voltage at which there is a 50-percent
probability of sparkover).
    Statistical withstand voltage. A transient overvoltage level that
produces a 0.14-percent probability of sparkover (that is, three
standard deviations below the voltage at which there is a 50-percent
probability of sparkover).
    Switch. A device for opening and closing or for changing the
connection of a circuit. In this subpart, a switch is manually
operable, unless otherwise stated.
    System operator. A qualified person designated to operate the
system or its parts.
    Vault. An enclosure, above or below ground, that personnel may
enter and that is used for installing, operating, or maintaining
equipment or cable.
    Vented vault. A vault that has provision for air changes using
exhaust-flue stacks and low-level air intakes operating on pressure and
temperature differentials that provide for airflow that precludes a
hazardous atmosphere from developing.
    Voltage. The effective (root mean square, or rms) potential
difference between any two conductors or between a conductor and
ground. This subpart expresses voltages in nominal values, unless
otherwise indicated. The nominal voltage of a system or circuit is the
value assigned to a system or circuit of a given voltage class for the
purpose of convenient designation. The operating voltage of the system
may vary above or below this value.
    Work-positioning equipment. A body belt or body harness system
rigged to allow an employee to be supported on an elevated vertical
surface, such as a utility pole or tower leg, and work with both hands
free while leaning.

Appendix A to Subpart V of Part 1926--[Reserved]

Appendix B to Subpart V of Part 1926--Working on Exposed Energized
Parts

I. Introduction

    Electric utilities design electric power generation,
transmission, and distribution installations to meet National
Electrical Safety Code (NESC), ANSI C2, requirements. Electric
utilities also design transmission and distribution lines to limit
line outages as required by system reliability criteria \1\ and to
withstand the maximum overvoltages impressed on the system.
Conditions such as switching surges, faults, and lightning can cause
overvoltages. Electric utilities generally select insulator design
and lengths and the clearances to structural parts so as to prevent
outages from contaminated line insulation and during storms. Line
insulator lengths and structural clearances have, over the years,
come closer to the minimum approach distances used by workers. As
minimum approach distances and structural clearances converge, it is
increasingly important that system designers and system operating
and maintenance personnel understand the

concepts underlying minimum approach distances.
---------------------------------------------------------------------------

    \1\ Federal, State, and local regulatory bodies and electric
utilities set reliability requirements that limit the number and
duration of system outages.
---------------------------------------------------------------------------

    The information in this appendix will assist employers in
complying with the minimum approach-distance requirements contained
in Sec. Sec.  1926.960(c)(1) and 1926.964(c). Employers must use the
technical criteria and methodology presented in this appendix in
establishing minimum approach distances in accordance with Sec.
1926.960(c)(1)(i) and Table V-2 and Table V-7. This appendix
provides essential background information and technical criteria for
the calculation of the required minimum approach distances for live-
line work on electric power generation, transmission, and
distribution installations.
    Unless an employer is using the maximum transient overvoltages
specified in Table V-8 for voltages over 72.5 kilovolts, the
employer must use persons knowledgeable in the techniques discussed
in this appendix, and competent in the field of electric
transmission and distribution system design, to determine the
maximum transient overvoltage.

II. General

    A. Definitions. The following definitions from Sec.  1926.968
relate to work on or near electric power generation, transmission,
and distribution lines and equipment and the electrical hazards they
present.
    Exposed. . . . Not isolated or guarded.
    Guarded. Covered, fenced, enclosed, or otherwise protected, by
means of suitable covers or casings, barrier rails or screens, mats,
or platforms, designed to minimize the possibility, under normal
conditions, of dangerous approach or inadvertent contact by persons
or objects.

    Note to the definition of ``guarded'': Wires that are insulated,
but not otherwise protected, are not guarded.

    Insulated. Separated from other conducting surfaces by a
dielectric (including air space) offering a high resistance to the
passage of current.

    Note to the definition of ``insulated'': When any object is said
to be insulated, it is understood to be insulated for the conditions
to which it normally is subjected. Otherwise, it is, for the purpose
of this subpart, uninsulated.

    Isolated. Not readily accessible to persons unless special means
for access are used.
    Statistical sparkover voltage. A transient overvoltage level
that produces a 97.72-percent probability of sparkover (that is, two
standard deviations above the voltage at which there is a 50-percent
probability of sparkover).
    Statistical withstand voltage. A transient overvoltage level
that produces a 0.14-percent probability of sparkover (that is,
three standard deviations below the voltage at which there is a 50-
percent probability of sparkover).
    B. Installations energized at 50 to 300 volts. The hazards posed
by installations energized at 50 to 300 volts are the same as those
found in many other workplaces. That is not to say that there is no
hazard, but the complexity of electrical protection required does
not compare to that required for high-voltage systems. The employee
must avoid contact with the exposed parts, and the protective
equipment used (such as rubber insulating gloves) must provide
insulation for the voltages involved.
    C. Exposed energized parts over 300 volts AC. Paragraph
(c)(1)(i) of Sec.  1926.960 requires the employer to establish
minimum approach distances no less than the distances computed by
Table V-2 for ac systems so that employees can work safely without
risk of sparkover.\2\
---------------------------------------------------------------------------

    \2\ Sparkover is a disruptive electric discharge in which an
electric arc forms and electric current passes through air.
---------------------------------------------------------------------------

    Unless the employee is using electrical protective equipment,
air is the insulating medium between the employee and energized
parts. The distance between the employee and an energized part must
be sufficient for the air to withstand the maximum transient
overvoltage that can reach the worksite under the working conditions
and practices the employee is using. This distance is the minimum
air insulation distance, and it is equal to the electrical component
of the minimum approach distance.
    Normal system design may provide or include a means (such as
lightning arrestors) to control maximum anticipated transient
overvoltages, or the employer may use temporary devices (portable
protective gaps) or measures (such as preventing automatic circuit
breaker reclosing) to achieve the same result. Paragraph (c)(1)(ii)
of Sec.  1926.960 requires the employer to determine the maximum
anticipated per-unit transient overvoltage, phase-to-ground, through
an engineering analysis or assume a maximum anticipated per-unit
transient overvoltage, phase-to-ground, in accordance with Table V-
8, which specifies the following maximums for ac systems:

72.6 to 420.0 kilovolts..................  3.5 per unit.
420.1 to 550.0 kilovolts.................  3.0 per unit.
550.1 to 800.0 kilovolts.................  2.5 per unit.

    See paragraph IV.A.2, later in this appendix, for additional
discussion of maximum transient overvoltages.
    D. Types of exposures. Employees working on or near energized
electric power generation, transmission, and distribution systems
face two kinds of exposures: Phase-to-ground and phase-to-phase. The
exposure is phase-to-ground: (1) With respect to an energized part,
when the employee is at ground potential or (2) with respect to
ground, when an employee is at the potential of the energized part
during live-line barehand work. The exposure is phase-to-phase, with
respect to an energized part, when an employee is at the potential
of another energized part (at a different potential) during live-
line barehand work.

III. Determination of Minimum Approach Distances for AC Voltages
Greater Than 300 Volts

    A. Voltages of 301 to 5,000 volts. Test data generally forms the
basis of minimum air insulation distances. The lowest voltage for
which sufficient test data exists is 5,000 volts, and these data
indicate that the minimum air insulation distance at that voltage is
20 millimeters (1 inch). Because the minimum air insulation distance
increases with increasing voltage, and, conversely, decreases with
decreasing voltage, an assumed minimum air insulation distance of 20
millimeters will protect against sparkover at voltages of 301 to
5,000 volts. Thus, 20 millimeters is the electrical component of the
minimum approach distance for these voltages.
    B. Voltages of 5.1 to 72.5 kilovolts. For voltages from 5.1 to
72.5 kilovolts, the Occupational Safety and Health Administration
bases the methodology for calculating the electrical component of
the minimum approach distance on Institute of Electrical and
Electronic Engineers (IEEE) Standard 4-1995, Standard Techniques for
High-Voltage Testing. Table 1 lists the critical sparkover distances
from that standard as listed in IEEE Std 516-2009, IEEE Guide for
Maintenance Methods on Energized Power Lines.

             Table 1--Sparkover Distance for Rod-to-Rod Gap
------------------------------------------------------------------------
   60 Hz rod-to-rod sparkover (kV      Gap spacing from IEEE Std 4-1995
               peak)                                 (cm)
------------------------------------------------------------------------
                        25                                    2
                        36                                    3
                        46                                    4
                        53                                    5
                        60                                    6
                        70                                    8
                        79                                   10
                        86                                   12
                        95                                   14
                       104                                   16
                       112                                   18
                       120                                   20
                       143                                   25
                       167                                   30
                       192                                   35
                       218                                   40
                       243                                   45
                       270                                   50
                       322                                   60
------------------------------------------------------------------------
Source: IEEE Std 516-2009.

    To use this table to determine the electrical component of the
minimum approach distance, the employer must determine the peak
phase-to-ground transient overvoltage and select a gap from the
table that corresponds to that voltage as a withstand voltage rather
than a critical sparkover voltage. To calculate the electrical
component of the minimum approach distance for voltages between 5
and 72.5 kilovolts, use the following procedure:
    1. Divide the phase-to-phase voltage by the square root of 3 to
convert it to a phase-to-ground voltage.
    2. Multiply the phase-to-ground voltage by the square root of 2
to convert the rms value of the voltage to the peak phase-to-ground
voltage.
    3. Multiply the peak phase-to-ground voltage by the maximum per-
unit transient overvoltage, which, for this voltage range, is 3.0,
as discussed later in this appendix. This is the maximum phase-to-
ground transient

overvoltage, which corresponds to the withstand voltage for the
relevant exposure.\3\
---------------------------------------------------------------------------

    \3\ The withstand voltage is the voltage at which sparkover is
not likely to occur across a specified distance. It is the voltage
taken at the 3[sigma] point below the sparkover voltage, assuming
that the sparkover curve follows a normal distribution.
---------------------------------------------------------------------------

    4. Divide the maximum phase-to-ground transient overvoltage by
0.85 to determine the corresponding critical sparkover voltage. (The
critical sparkover voltage is 3 standard deviations (or 15 percent)
greater than the withstand voltage.)
    5. Determine the electrical component of the minimum approach
distance from Table 1 through interpolation.
    Table 2 illustrates how to derive the electrical component of
the minimum approach distance for voltages from 5.1 to 72.5
kilovolts, before the application of any altitude correction factor,
as explained later.

                     Table 2--Calculating the Electrical Component of MAD--751 V to 72.5 kV
----------------------------------------------------------------------------------------------------------------
                                                            Maximum system phase-to-phase voltage (kV)
                      Step                       ---------------------------------------------------------------
                                                        15              36              46             72.5
----------------------------------------------------------------------------------------------------------------
1. Divide by [radic]3...........................             8.7            20.8            26.6            41.9
2. Multiply by [radic]3.........................            12.2            29.4            37.6            59.2
3. Multiply by 3.0..............................            36.7            88.2           112.7           177.6
4. Divide by 0.85...............................            43.2           103.7           132.6           208.9
5. Interpolate from Table 1.....................    3+(7.2/10)*1    14+(8.7/9)*2  20+(12.6/23)*5  35+(16.9/26)*5
Electrical component of MAD (cm)................            3.72           15.93           22.74           38.25
----------------------------------------------------------------------------------------------------------------

    C. Voltages of 72.6 to 800 kilovolts. For voltages of 72.6
kilovolts to 800 kilovolts, this subpart bases the electrical
component of minimum approach distances, before the application of
any altitude correction factor, on the following formula:

Equation 1--For voltages of 72.6 kV to 800 kV

D = 0.3048(C + a)VL-GT

Where:

D = Electrical component of the minimum approach distance in air in
meters;
C = a correction factor associated with the variation of gap
sparkover with voltage;
    a = A factor relating to the saturation of air at system
voltages of 345 kilovolts or higher; \4\
---------------------------------------------------------------------------

    \4\ Test data demonstrates that the saturation factor is greater
than 0 at peak voltages of about 630 kilovolts. Systems operating at
345 kilovolts (or maximum system voltages of 362 kilovolts) can have
peak maximum transient overvoltages exceeding 630 kilovolts. Table
V-2 sets equations for calculating a based on peak voltage.
---------------------------------------------------------------------------

    VL-G = Maximum system line-to-ground rms voltage in kilovolts--
it should be the ``actual'' maximum, or the normal highest voltage
for the range (for example, 10 percent above the nominal voltage);
and
T = Maximum transient overvoltage factor in per unit.

    In Equation 1, C is 0.01: (1) For phase-to-ground exposures that
the employer can demonstrate consist only of air across the approach
distance (gap) and (2) for phase-to-phase exposures if the employer
can demonstrate that no insulated tool spans the gap and that no
large conductive object is in the gap. Otherwise, C is 0.011.
    In Equation 1, the term a varies depending on whether the
employee's exposure is phase-to-ground or phase-to-phase and on
whether objects are in the gap. The employer must use the equations
in Table 3 to calculate a. Sparkover test data with insulation
spanning the gap form the basis for the equations for phase-to-
ground exposures, and sparkover test data with only air in the gap
form the basis for the equations for phase-to-phase exposures. The
phase-to-ground equations result in slightly higher values of a,
and, consequently, produce larger minimum approach distances, than
the phase-to-phase equations for the same value of VPeak.

[GRAPHIC] [TIFF OMITTED] TR11AP14.036

    In Equation 1, T is the maximum transient overvoltage factor in
per unit. As noted earlier, Sec.  1926.960(c)(1)(ii) requires the
employer to determine the maximum anticipated per-unit transient
overvoltage, phase-to-ground, through an engineering analysis or
assume a maximum anticipated per-unit transient overvoltage, phase-
to-ground, in accordance with Table V-8. For phase-to-ground
exposures, the employer uses this value, called TL-G, as T in
Equation 1. IEEE Std 516-2009 provides the following formula to
calculate the phase-to-phase maximum transient overvoltage, TL-L,
from TL-G:

TL-L = 1.35TL-G + 0.45.

For phase-to-phase exposures, the employer uses this value as T in
Equation 1.
    D. Provisions for inadvertent movement. The minimum approach
distance must include an ``adder'' to compensate for the inadvertent
movement of the worker relative to an energized part or the movement
of the part relative to the worker. This ``adder'' must account for
this possible inadvertent movement and provide the worker with a
comfortable and safe zone in which to work. Employers must add the
distance for inadvertent movement (called the ``ergonomic component
of the minimum approach distance'') to the electrical component to
determine the total safe minimum approach distances used in live-
line work.
    The Occupational Safety and Health Administration based the
ergonomic component of the minimum approach distance on response
time-distance analysis. This technique uses an estimate of the total
response time to a hazardous incident and converts that time to the
distance traveled. For example, the driver of a car takes a given
amount of time to respond to a ``stimulus'' and stop the vehicle.
The elapsed time involved results in the car's traveling some
distance before coming to a complete stop. This distance depends on
the speed of the car at the time the stimulus appears and the
reaction time of the driver.
    In the case of live-line work, the employee must first perceive
that he or she is approaching the danger zone. Then, the worker
responds to the danger and must decelerate and stop all motion
toward the energized part. During the time it takes to stop, the
employee will travel some distance. This is the distance the
employer must add to the electrical component of the minimum
approach distance to obtain the total safe minimum approach
distance.
    At voltages from 751 volts to 72.5 kilovolts,\5\ the electrical
component of the minimum approach distance is smaller than the
ergonomic component. At 72.5 kilovolts, the electrical component is
only a little more than 0.3 meters (1 foot). An ergonomic component
of the minimum approach distance must provide for all the worker's
unanticipated movements. At these voltages, workers generally use
rubber insulating gloves; however, these gloves protect only a
worker's hands and arms. Therefore, the energized object must be at
a safe approach distance to protect the worker's face. In this case,
0.61 meters (2 feet) is a sufficient and practical ergonomic
component of the minimum approach distance.
---------------------------------------------------------------------------

    \5\ For voltages of 50 to 300 volts, Table V-2 specifies a
minimum approach distance of ``avoid contact.'' The minimum approach
distance for this voltage range contains neither an electrical
component nor an ergonomic component.
---------------------------------------------------------------------------

    For voltages between 72.6 and 800 kilovolts, employees must use
different work practices during energized line work. Generally,
employees use live-line tools (hot sticks) to perform work on
energized equipment. These tools, by design, keep the energized part
at a constant distance from the employee and, thus, maintain the
appropriate minimum approach distance automatically.
    The location of the worker and the type of work methods the
worker is using also influence the length of the ergonomic component
of the minimum approach distance. In this higher voltage range, the
employees use work methods that more tightly control their movements
than when the workers perform work using rubber insulating gloves.
The worker, therefore, is farther from the energized line or
equipment and must be more precise in his or her movements just to
perform the work. For these reasons, this subpart adopts an
ergonomic component of the minimum approach distance of 0.31 m (1
foot) for voltages between 72.6 and 800 kilovolts.
    Table 4 summarizes the ergonomic component of the minimum
approach distance for various voltage ranges.

        Table 4--Ergonomic Component of Minimum Approach Distance
------------------------------------------------------------------------
                                                   Distance
         Voltage range (kV)          -----------------------------------
                                              m                ft
------------------------------------------------------------------------
0.301 to 0.750......................              0.31               1.0
0.751 to 72.5.......................              0.61               2.0
72.6 to 800.........................              0.31               1.0
------------------------------------------------------------------------
Note: The employer must add this distance to the electrical component of
  the minimum approach distance to obtain the full minimum approach
  distance.

    The ergonomic component of the minimum approach distance
accounts for errors in maintaining the minimum approach distance
(which might occur, for example, if an employee misjudges the length
of a conductive object he or she is holding), and for errors in
judging the minimum approach distance. The ergonomic component also
accounts for inadvertent movements by the employee, such as
slipping. In contrast, the working position selected to properly
maintain the minimum approach distance must account for all of an
employee's reasonably likely movements and still permit the employee
to adhere to the applicable minimum approach distance. (See Figure
1.) Reasonably likely movements include an employee's adjustments to
tools, equipment, and working positions and all movements needed to
perform the work. For example, the employee should be able to
perform all of the following actions without straying into the
minimum approach distance:
     Adjust his or her hardhat,
     maneuver a tool onto an energized part with a
reasonable amount of overreaching or underreaching,
     reach for and handle tools, material, and equipment
passed to him or her, and
     adjust tools, and replace components on them, when
necessary during the work procedure.
    The training of qualified employees required under Sec.
1926.950, and the job planning and briefing required under Sec.
1926.952, must address selection of a proper working position.
BILLING CODE 4510-26-P

[GRAPHIC] [TIFF OMITTED] TR11AP14.037

BILLING CODE 4510-26-C
    E. Miscellaneous correction factors. Changes in the air medium
that forms the insulation influences the strength of an air gap. A
brief discussion of each factor follows.
    1. Dielectric strength of air. The dielectric strength of air in
a uniform electric field at standard atmospheric conditions is
approximately 3 kilovolts per millimeter.\6\ The pressure,
temperature, and humidity of the air, the shape, dimensions, and
separation of the electrodes, and the

characteristics of the applied voltage (wave shape) affect the
disruptive gradient.
---------------------------------------------------------------------------

    \6\ For the purposes of estimating arc length, Subpart V
generally assumes a more conservative dielectric strength of 10
kilovolts per 25.4 millimeters, consistent with assumptions made in
consensus standards such as the National Electrical Safety Code
(IEEE C2-2012). The more conservative value accounts for variables
such as electrode shape, wave shape, and a certain amount of
overvoltage.
---------------------------------------------------------------------------

    2. Atmospheric effect. The empirically determined electrical
strength of a given gap is normally applicable at standard
atmospheric conditions (20 [deg]C, 101.3 kilopascals, 11 grams/cubic
centimeter humidity). An increase in the density (humidity) of the
air inhibits sparkover for a given air gap. The combination of
temperature and air pressure that results in the lowest gap
sparkover voltage is high temperature and low pressure. This
combination of conditions is not likely to occur. Low air pressure,
generally associated with high humidity, causes increased electrical
strength. An average air pressure generally correlates with low
humidity. Hot and dry working conditions normally result in reduced
electrical strength. The equations for minimum approach distances in
Table V-2 assume standard atmospheric conditions.
    3. Altitude. The reduced air pressure at high altitudes causes a
reduction in the electrical strength of an air gap. An employer must
increase the minimum approach distance by about 3 percent per 300
meters (1,000 feet) of increased altitude for altitudes above 900
meters (3,000 feet). Table V-4 specifies the altitude correction
factor that the employer must use in calculating minimum approach
distances.

IV. Determining Minimum Approach Distances

A. Factors Affecting Voltage Stress at the Worksite

    1. System voltage (nominal). The nominal system voltage range
determines the voltage for purposes of calculating minimum approach
distances. The employer selects the range in which the nominal
system voltage falls, as given in the relevant table, and uses the
highest value within that range in per-unit calculations.
    2. Transient overvoltages. Operation of switches or circuit
breakers, a fault on a line or circuit or on an adjacent circuit,
and similar activities may generate transient overvoltages on an
electrical system. Each overvoltage has an associated transient
voltage wave shape. The wave shape arriving at the site and its
magnitude vary considerably.
    In developing requirements for minimum approach distances, the
Occupational Safety and Health Administration considered the most
common wave shapes and the magnitude of transient overvoltages found
on electric power generation, transmission, and distribution
systems. The equations in Table V-2 for minimum approach distances
use per-unit maximum transient overvoltages, which are relative to
the nominal maximum voltage of the system. For example, a maximum
transient overvoltage value of 3.0 per unit indicates that the
highest transient overvoltage is 3.0 times the nominal maximum
system voltage.
    3. Typical magnitude of overvoltages. Table 5 lists the
magnitude of typical transient overvoltages.

          Table 5--Magnitude of Typical Transient Overvoltages
------------------------------------------------------------------------
                                                         Magnitude  (per
                         Cause                                unit)
------------------------------------------------------------------------
Energized 200-mile line without closing resistors.....               3.5
Energized 200-mile line with one-step closing resistor               2.1
Energized 200-mile line with multistep resistor.......               2.5
Reclosing with trapped charge one-step resistor.......               2.2
Opening surge with single restrike....................               3.0
Fault initiation unfaulted phase......................               2.1
Fault initiation adjacent circuit.....................               2.5
Fault clearing........................................        1.7 to 1.9
------------------------------------------------------------------------

    4. Standard deviation--air-gap withstand. For each air gap
length under the same atmospheric conditions, there is a statistical
variation in the breakdown voltage. The probability of breakdown
against voltage has a normal (Gaussian) distribution. The standard
deviation of this distribution varies with the wave shape, gap
geometry, and atmospheric conditions. The withstand voltage of the
air gap is three standard deviations (3[sigma]) below the critical
sparkover voltage. (The critical sparkover voltage is the crest
value of the impulse wave that, under specified conditions, causes
sparkover 50 percent of the time. An impulse wave of three standard
deviations below this value, that is, the withstand voltage, has a
probability of sparkover of approximately 1 in 1,000.)
    5. Broken Insulators. Tests show reductions in the insulation
strength of insulator strings with broken skirts. Broken units may
lose up to 70 percent of their withstand capacity. Because an
employer cannot determine the insulating capability of a broken unit
without testing it, the employer must consider damaged units in an
insulator to have no insulating value. Additionally, the presence of
a live-line tool alongside an insulator string with broken units may
further reduce the overall insulating strength. The number of good
units that must be present in a string for it to be ``insulated'' as
defined by Sec.  1926.968 depends on the maximum overvoltage
possible at the worksite.

B. Minimum Approach Distances Based on Known, Maximum-Anticipated
Per-Unit Transient Overvoltages

    1. Determining the minimum approach distance for AC systems.
Under Sec.  1926.960(c)(1)(ii), the employer must determine the
maximum anticipated per-unit transient overvoltage, phase-to-ground,
through an engineering analysis or must assume a maximum anticipated
per-unit transient overvoltage, phase-to-ground, in accordance with
Table V-8. When the employer conducts an engineering analysis of the
system and determines that the maximum transient overvoltage is
lower than specified by Table V-8, the employer must ensure that any
conditions assumed in the analysis, for example, that employees
block reclosing on a circuit or install portable protective gaps,
are present during energized work. To ensure that these conditions
are present, the employer may need to institute new live-work
procedures reflecting the conditions and limitations set by the
engineering analysis.
    2. Calculation of reduced approach distance values. An employer
may take the following steps to reduce minimum approach distances
when the maximum transient overvoltage on the system (that is, the
maximum transient overvoltage without additional steps to control
overvoltages) produces unacceptably large minimum approach
distances:
    Step 1. Determine the maximum voltage (with respect to a given
nominal voltage range) for the energized part.
    Step 2. Determine the technique to use to control the maximum
transient overvoltage. (See paragraphs IV.C and IV.D of this
appendix.) Determine the maximum transient overvoltage that can
exist at the worksite with that form of control in place and with a
confidence level of 3[sigma] . This voltage is the withstand voltage
for the purpose of calculating the appropriate minimum approach
distance.
    Step 3. Direct employees to implement procedures to ensure that
the control technique is in effect during the course of the work.
    Step 4. Using the new value of transient overvoltage in per
unit, calculate the required minimum approach distance from Table V-
2.

C. Methods of Controlling Possible Transient Overvoltage Stress
Found on a System

    1. Introduction. There are several means of controlling
overvoltages that occur on transmission systems. For example, the
employer can modify the operation of circuit breakers or other
switching devices to reduce switching transient overvoltages.
Alternatively, the employer can hold the overvoltage to an
acceptable level by installing surge arresters or portable

protective gaps on the system. In addition, the employer can change
the transmission system to minimize the effect of switching
operations. Section 4.8 of IEEE Std 516-2009 describes various ways
of controlling, and thereby reducing, maximum transient
overvoltages.
    2. Operation of circuit breakers.\7\ The maximum transient
overvoltage that can reach the worksite is often the result of
switching on the line on which employees are working. Disabling
automatic reclosing during energized line work, so that the line
will not be reenergized after being opened for any reason, limits
the maximum switching surge overvoltage to the larger of the opening
surge or the greatest possible fault-generated surge, provided that
the devices (for example, insertion resistors) are operable and will
function to limit the transient overvoltage and that circuit breaker
restrikes do not occur. The employer must ensure the proper
functioning of insertion resistors and other overvoltage-limiting
devices when the employer's engineering analysis assumes their
proper operation to limit the overvoltage level. If the employer
cannot disable the reclosing feature (because of system operating
conditions), other methods of controlling the switching surge level
may be necessary.
---------------------------------------------------------------------------

    \7\ The detailed design of a circuit interrupter, such as the
design of the contacts, resistor insertion, and breaker timing
control, are beyond the scope of this appendix. The design of the
system generally accounts for these features. This appendix only
discusses features that can limit the maximum switching transient
overvoltage on a system.
---------------------------------------------------------------------------

    Transient surges on an adjacent line, particularly for double
circuit construction, may cause a significant overvoltage on the
line on which employees are working. The employer's engineering
analysis must account for coupling to adjacent lines.
    3. Surge arresters. The use of modern surge arresters allows a
reduction in the basic impulse-insulation levels of much
transmission system equipment. The primary function of early
arresters was to protect the system insulation from the effects of
lightning. Modern arresters not only dissipate lightning-caused
transients, but may also control many other system transients caused
by switching or faults.
    The employer may use properly designed arresters to control
transient overvoltages along a transmission line and thereby reduce
the requisite length of the insulator string and possibly the
maximum transient overvoltage on the line.\8\
---------------------------------------------------------------------------

    \8\ Surge arrester application is beyond the scope of this
appendix. However, if the employer installs the arrester near the
work site, the application would be similar to the protective gaps
discussed in paragraph IV.D of this appendix.
---------------------------------------------------------------------------

    4. Switching Restrictions. Another form of overvoltage control
involves establishing switching restrictions, whereby the employer
prohibits the operation of circuit breakers until certain system
conditions are present. The employer restricts switching by using a
tagging system, similar to that used for a permit, except that the
common term used for this activity is a ``hold-off'' or
``restriction.'' These terms indicate that the restriction does not
prevent operation, but only modifies the operation during the live-
work activity.

D. Minimum Approach Distance Based on Control of Maximum Transient
Overvoltage at the Worksite

    When the employer institutes control of maximum transient
overvoltage at the worksite by installing portable protective gaps,
the employer may calculate the minimum approach distance as follows:
    Step 1. Select the appropriate withstand voltage for the
protective gap based on system requirements and an acceptable
probability of gap sparkover.\9\
---------------------------------------------------------------------------

    \9\ The employer should check the withstand voltage to ensure
that it results in a probability of gap flashover that is acceptable
from a system outage perspective. (In other words, a gap sparkover
will produce a system outage. The employer should determine whether
such an outage will impact overall system performance to an
acceptable degree.) In general, the withstand voltage should be at
least 1.25 times the maximum crest operating voltage.
---------------------------------------------------------------------------

    Step 2. Determine a gap distance that provides a withstand
voltage \10\ greater than or equal to the one selected in the first
step.\11\
---------------------------------------------------------------------------

    \10\ The manufacturer of the gap provides, based on test data,
the critical sparkover voltage for each gap spacing (for example, a
critical sparkover voltage of 665 kilovolts for a gap spacing of 1.2
meters). The withstand voltage for the gap is equal to 85 percent of
its critical sparkover voltage.
    \11\ Switch steps 1 and 2 if the length of the protective gap is
known.
---------------------------------------------------------------------------

    Step 3. Use 110 percent of the gap's critical sparkover voltage
to determine the phase-to-ground peak voltage at gap sparkover (VPPG
Peak).
    Step 4. Determine the maximum transient overvoltage, phase-to-
ground, at the worksite from the following formula:
[GRAPHIC] [TIFF OMITTED] TR11AP14.038

    Step 5. Use this value of T \12\ in the equation in Table V-2 to
obtain the minimum approach distance. If the worksite is no more
than 900 meters (3,000 feet) above sea level, the employer may use
this value of T to determine the minimum approach distance from
Table 7 through Table 14.
---------------------------------------------------------------------------

    \12\ IEEE Std 516-2009 states that most employers add 0.2 to the
calculated value of T as an additional safety factor.

    Note: All rounding must be to the next higher value (that is,
---------------------------------------------------------------------------
always round up).

    Sample protective gap calculations.
    Problem: Employees are to perform work on a 500-kilovolt
transmission line at sea level that is subject to transient
overvoltages of 2.4 p.u. The maximum operating voltage of the line
is 550 kilovolts. Determine the length of the protective gap that
will provide the minimum practical safe approach distance. Also,
determine what that minimum approach distance is.
    Step 1. Calculate the smallest practical maximum transient
overvoltage (1.25 times the crest phase-to-ground voltage): \13\
---------------------------------------------------------------------------

    \13\ To eliminate sparkovers due to minor system disturbances,
the employer should use a withstand voltage no lower than 1.25 p.u.
Note that this is a practical, or operational, consideration only.
It may be feasible for the employer to use lower values of withstand
voltage.
[GRAPHIC] [TIFF OMITTED] TR11AP14.039

This value equals the withstand voltage of the protective gap.
    Step 2. Using test data for a particular protective gap, select
a gap that has a critical sparkover voltage greater than or equal
to:

561kV / 0.85 = 660kV

For example, if a protective gap with a 1.22-m (4.0-foot) spacing
tested to a critical sparkover voltage of 665 kilovolts (crest),
select this gap spacing.
    Step 3. The phase-to-ground peak voltage at gap sparkover (VPPG
Peak) is 110 percent of the value from the previous step:

665kVx 1.10 = 732kV

This value corresponds to the withstand voltage of the electrical
component of the minimum approach distance.
    Step 4. Use this voltage to determine the worksite value of T:
    [GRAPHIC] [TIFF OMITTED] TR11AP14.040

    Step 5. Use this value of T in the equation in Table V-2 to
obtain the minimum approach distance, or look up the minimum
approach distance in Table 7 through Table 14:

MAD = 2.29m(7.6ft)

E. Location of Protective Gaps

    1. Adjacent structures. The employer may install the protective
gap on a structure adjacent to the worksite, as this practice does
not significantly reduce the protection afforded by the gap.
    2. Terminal stations. Gaps installed at terminal stations of
lines or circuits provide a level of protection; however, that level
of protection may not extend throughout the length of the line to
the worksite. The use of substation terminal gaps raises the
possibility that separate surges could enter the line at opposite
ends, each with low enough magnitude to pass the terminal gaps
without sparkover. When voltage surges occur simultaneously at each
end of a line and travel toward each other, the total voltage on the
line at the point where they meet is the arithmetic sum of the two
surges. A gap installed within 0.8 km (0.5 mile) of the worksite
will protect against such intersecting waves. Engineering studies of
a particular line or system may indicate that employers can
adequately protect employees by installing gaps at even more distant
locations. In any event, unless using the default values for T from
Table V-8, the employer must determine T at the worksite.
    3. Worksite. If the employer installs protective gaps at the
worksite, the gap setting establishes the worksite impulse
insulation strength. Lightning strikes as far as 6 miles from the
worksite can cause a voltage surge greater than the gap withstand
voltage, and a gap sparkover can occur. In addition, the gap can
sparkover from overvoltages on the line that exceed the withstand
voltage of the gap. Consequently, the employer must protect
employees from hazards resulting from any sparkover that could
occur.

    F. Disabling automatic reclosing. There are two reasons to
disable the automatic-reclosing feature of circuit-interrupting
devices while employees are performing live-line work:
     To prevent reenergization of a circuit faulted during
the work, which could create a hazard or result in more serious
injuries or damage than the injuries or damage produced by the
original fault;
     To prevent any transient overvoltage caused by the
switching surge that would result if the circuit were reenergized.
    However, due to system stability considerations, it may not
always be feasible to disable the automatic-reclosing feature.

V. Minimum Approach-Distance Tables

    A. Legacy tables. Employers may use the minimum approach
distances in Table 6 until March 31, 2015.

                            Table 6--Minimum Approach Distances Until March 31, 2015
----------------------------------------------------------------------------------------------------------------
                                                     Phase-to-ground exposure         Phase-to-phase exposure
       Voltage range phase to phase (kV)        ----------------------------------------------------------------
                                                        m               ft               m              ft
----------------------------------------------------------------------------------------------------------------
2.1 to 15.0....................................            0.64             2.1             0.61             2.0
15.1 to 35.0...................................            0.71             2.3             0.71             2.3
35.1 to 46.0...................................            0.76             2.5             0.76             2.5
46.1 to 72.5...................................            0.91             3.0             0.91             3.0
72.6 to 121....................................            1.02             3.3             1.37             4.5
138 to 145.....................................            1.07             3.5             1.52             5.0
161 to 169.....................................            1.12             3.7             1.68             5.5
230 to 242.....................................            1.52             5.0             2.54             8.3
345 to 362 *...................................            2.13             7.0             4.06            13.3
500 to 552 *...................................            3.35            11.0             6.10            20.0
700 to 765 *...................................            4.57            15.0             9.45            31.0
----------------------------------------------------------------------------------------------------------------
* The minimum approach distance may be the shortest distance between the energized part and the grounded
  surface.

    B. Alternative minimum approach distances. Employers may use the
minimum approach distances in Table 7 through Table 14 provided that
the employer follows the notes to those tables.

                            Table 7--AC Minimum Approach Distances--72.6 to 121.0 kV
----------------------------------------------------------------------------------------------------------------
                                                     Phase-to-ground exposure         Phase-to-phase exposure
                    T (p.u.)                    ----------------------------------------------------------------
                                                        m               ft               m              ft
----------------------------------------------------------------------------------------------------------------
1.5............................................            0.67             2.2             0.84             2.8
1.6............................................            0.69             2.3             0.87             2.9
1.7............................................            0.71             2.3             0.90             3.0
1.8............................................            0.74             2.4             0.93             3.1
1.9............................................            0.76             2.5             0.96             3.1
2.0............................................            0.78             2.6             0.99             3.2
2.1............................................            0.81             2.7             1.01             3.3
2.2............................................            0.83             2.7             1.04             3.4
2.3............................................            0.85             2.8             1.07             3.5
2.4............................................            0.88             2.9             1.10             3.6
2.5............................................            0.90             3.0             1.13             3.7
2.6............................................            0.92             3.0             1.16             3.8
2.7............................................            0.95             3.1             1.19             3.9
2.8............................................            0.97             3.2             1.22             4.0
2.9............................................            0.99             3.2             1.24             4.1
3.0............................................            1.02             3.3             1.27             4.2
3.1............................................            1.04             3.4             1.30             4.3
3.2............................................            1.06             3.5             1.33             4.4
3.3............................................            1.09             3.6             1.36             4.5
3.4............................................            1.11             3.6             1.39             4.6
3.5............................................            1.13             3.7             1.42             4.7
----------------------------------------------------------------------------------------------------------------

                            Table 8--AC Minimum Approach Distances--121.1 to 145.0 kV
----------------------------------------------------------------------------------------------------------------
                                                     Phase-to-ground rxposure         Phase-to-phase rxposure
                    T (p.u.)                    ----------------------------------------------------------------
                                                        m               ft               m              ft
----------------------------------------------------------------------------------------------------------------
1.5............................................            0.74             2.4             0.95             3.1
1.6............................................            0.76             2.5             0.98             3.2
1.7............................................            0.79             2.6             1.02             3.3
1.8............................................            0.82             2.7             1.05             3.4
1.9............................................            0.85             2.8             1.08             3.5
2.0............................................            0.88             2.9             1.12             3.7
2.1............................................            0.90             3.0             1.15             3.8
2.2............................................            0.93             3.1             1.19             3.9

2.3............................................            0.96             3.1             1.22             4.0
2.4............................................            0.99             3.2             1.26             4.1
2.5............................................            1.02             3.3             1.29             4.2
2.6............................................            1.04             3.4             1.33             4.4
2.7............................................            1.07             3.5             1.36             4.5
2.8............................................            1.10             3.6             1.39             4.6
2.9............................................            1.13             3.7             1.43             4.7
3.0............................................            1.16             3.8             1.46             4.8
3.1............................................            1.19             3.9             1.50             4.9
3.2............................................            1.21             4.0             1.53             5.0
3.3............................................            1.24             4.1             1.57             5.2
3.4............................................            1.27             4.2             1.60             5.2
3.5............................................            1.30             4.3             1.64             5.4
----------------------------------------------------------------------------------------------------------------

                            Table 9--AC Minimum Approach Distances--145.1 to 169.0 kV
----------------------------------------------------------------------------------------------------------------
                                                     Phase-to-ground exposure         Phase-to-phase exposure
                    T (p.u.)                    ----------------------------------------------------------------
                                                        m               ft               m              ft
----------------------------------------------------------------------------------------------------------------
1.5............................................            0.81             2.7             1.05             3.4
1.6............................................            0.84             2.8             1.09             3.6
1.7............................................            0.87             2.9             1.13             3.7
1.8............................................            0.90             3.0             1.17             3.8
1.9............................................            0.94             3.1             1.21             4.0
2.0............................................            0.97             3.2             1.25             4.1
2.1............................................            1.00             3.3             1.29             4.2
2.2............................................            1.03             3.4             1.33             4.4
2.3............................................            1.07             3.5             1.37             4.5
2.4............................................            1.10             3.6             1.41             4.6
2.5............................................            1.13             3.7             1.45             4.8
2.6............................................            1.17             3.8             1.49             4.9
2.7............................................            1.20             3.9             1.53             5.0
2.8............................................            1.23             4.0             1.57             5.2
2.9............................................            1.26             4.1             1.61             5.3
3.0............................................            1.30             4.3             1.65             5.4
3.1............................................            1.33             4.4             1.70             5.6
3.2............................................            1.36             4.5             1.76             5.8
3.3............................................            1.39             4.6             1.82             6.0
3.4............................................            1.43             4.7             1.88             6.2
3.5............................................            1.46             4.8             1.94             6.4
----------------------------------------------------------------------------------------------------------------

                           Table 10--AC Minimum Approach Distances--169.1 to 242.0 kV
----------------------------------------------------------------------------------------------------------------
                                                     Phase-to-ground exposure         Phase-to-phase exposure
                    T (p.u.)                    ----------------------------------------------------------------
                                                        m               ft               m              ft
----------------------------------------------------------------------------------------------------------------
1.5............................................            1.02             3.3             1.37             4.5
1.6............................................            1.06             3.5             1.43             4.7
1.7............................................            1.11             3.6             1.48             4.9
1.8............................................            1.16             3.8             1.54             5.1
1.9............................................            1.21             4.0             1.60             5.2
2.0............................................            1.25             4.1             1.66             5.4
2.1............................................            1.30             4.3             1.73             5.7
2.2............................................            1.35             4.4             1.81             5.9
2.3............................................            1.39             4.6             1.90             6.2
2.4............................................            1.44             4.7             1.99             6.5
2.5............................................            1.49             4.9             2.08             6.8
2.6............................................            1.53             5.0             2.17             7.1
2.7............................................            1.58             5.2             2.26             7.4
2.8............................................            1.63             5.3             2.36             7.7
2.9............................................            1.67             5.5             2.45             8.0
3.0............................................            1.72             5.6             2.55             8.4
3.1............................................            1.77             5.8             2.65             8.7
3.2............................................            1.81             5.9             2.76             9.1
3.3............................................            1.88             6.2             2.86             9.4
3.4............................................            1.95             6.4             2.97             9.7
3.5............................................            2.01             6.6             3.08            10.1
----------------------------------------------------------------------------------------------------------------

                           Table 11--AC Minimum Approach Distances--242.1 to 362.0 kV
----------------------------------------------------------------------------------------------------------------
                                                     Phase-to-ground exposure         Phase-to-phase exposure
                    T (p.u.)                    ----------------------------------------------------------------
                                                        m               ft               m              ft
----------------------------------------------------------------------------------------------------------------
1.5............................................            1.37             4.5             1.99             6.5
1.6............................................            1.44             4.7             2.13             7.0
1.7............................................            1.51             5.0             2.27             7.4
1.8............................................            1.58             5.2             2.41             7.9
1.9............................................            1.65             5.4             2.56             8.4
2.0............................................            1.72             5.6             2.71             8.9
2.1............................................            1.79             5.9             2.87             9.4
2.2............................................            1.87             6.1             3.03             9.9
2.3............................................            1.97             6.5             3.20            10.5
2.4............................................            2.08             6.8             3.37            11.1
2.5............................................            2.19             7.2             3.55            11.6
2.6............................................            2.29             7.5             3.73            12.2
2.7............................................            2.41             7.9             3.91            12.8
2.8............................................            2.52             8.3             4.10            13.5
2.9............................................            2.64             8.7             4.29            14.1
3.0............................................            2.76             9.1             4.49            14.7
3.1............................................            2.88             9.4             4.69            15.4
3.2............................................            3.01             9.9             4.90            16.1
3.3............................................            3.14            10.3             5.11            16.8
3.4............................................            3.27            10.7             5.32            17.5
3.5............................................            3.41            11.2             5.52            18.1
----------------------------------------------------------------------------------------------------------------

                           Table 12--AC Minimum Approach Distances--362.1 to 420.0 kV
----------------------------------------------------------------------------------------------------------------
                                                     Phase-to-ground exposure         Phase-to-phase exposure
                    T (p.u.)                    ----------------------------------------------------------------
                                                        m               ft               m              ft
----------------------------------------------------------------------------------------------------------------
1.5............................................            1.53             5.0             2.40             7.9
1.6............................................            1.62             5.3             2.58             8.5
1.7............................................            1.70             5.6             2.75             9.0
1.8............................................            1.78             5.8             2.94             9.6
1.9............................................            1.88             6.2             3.13            10.3
2.0............................................            1.99             6.5             3.33            10.9
2.1............................................            2.12             7.0             3.53            11.6
2.2............................................            2.24             7.3             3.74            12.3
2.3............................................            2.37             7.8             3.95            13.0
2.4............................................            2.50             8.2             4.17            13.7
2.5............................................            2.64             8.7             4.40            14.4
2.6............................................            2.78             9.1             4.63            15.2
2.7............................................            2.93             9.6             4.87            16.0
2.8............................................            3.07            10.1             5.11            16.8
2.9............................................            3.23            10.6             5.36            17.6
3.0............................................            3.38            11.1             5.59            18.3
3.1............................................            3.55            11.6             5.82            19.1
3.2............................................            3.72            12.2             6.07            19.9
3.3............................................            3.89            12.8             6.31            20.7
3.4............................................            4.07            13.4             6.56            21.5
3.5............................................            4.25            13.9             6.81            22.3
----------------------------------------------------------------------------------------------------------------

                           Table 13--AC Minimum Approach Distances--420.1 to 550.0 kV
----------------------------------------------------------------------------------------------------------------
                                                     Phase-to-ground exposure         Phase-to-phase exposure
                    T (p.u.)                    ----------------------------------------------------------------
                                                        m               ft               m              ft
----------------------------------------------------------------------------------------------------------------
1.5............................................            1.95             6.4             3.46            11.4
1.6............................................            2.11             6.9             3.73            12.2
1.7............................................            2.28             7.5             4.02            13.2
1.8............................................            2.45             8.0             4.31            14.1
1.9............................................            2.62             8.6             4.61            15.1
2.0............................................            2.81             9.2             4.92            16.1
2.1............................................            3.00             9.8             5.25            17.2
2.2............................................            3.20            10.5             5.55            18.2
2.3............................................            3.40            11.2             5.86            19.2
2.4............................................            3.62            11.9             6.18            20.3
2.5............................................            3.84            12.6             6.50            21.3
2.6............................................            4.07            13.4             6.83            22.4
2.7............................................            4.31            14.1             7.18            23.6

2.8............................................            4.56            15.0             7.52            24.7
2.9............................................            4.81            15.8             7.88            25.9
3.0............................................            5.07            16.6             8.24            27.0
----------------------------------------------------------------------------------------------------------------

                           Table 14--AC Minimum Approach Distances--550.1 to 800.0 kV
----------------------------------------------------------------------------------------------------------------
                                                     Phase-to-ground exposure         Phase-to-phase exposure
                    T (p.u.)                    ----------------------------------------------------------------
                                                        m               ft               m              ft
----------------------------------------------------------------------------------------------------------------
1.5............................................            3.16            10.4             5.97            19.6
1.6............................................            3.46            11.4             6.43            21.1
1.7............................................            3.78            12.4             6.92            22.7
1.8............................................            4.12            13.5             7.42            24.3
1.9............................................            4.47            14.7             7.93            26.0
2.0............................................            4.83            15.8             8.47            27.8
2.1............................................            5.21            17.1             9.02            29.6
2.2............................................            5.61            18.4             9.58            31.4
2.3............................................            6.02            19.8            10.16            33.3
2.4............................................            6.44            21.1            10.76            35.3
2.5............................................            6.88            22.6            11.38            37.3
----------------------------------------------------------------------------------------------------------------
Notes to Table 7 through Table 14:
1. The employer must determine the maximum anticipated per-unit transient overvoltage, phase-to-ground, through
  an engineering analysis, as required by Sec.   1926.960(c)(1)(ii), or assume a maximum anticipated per-unit
  transient overvoltage, phase-to-ground, in accordance with Table V-8.
2. For phase-to-phase exposures, the employer must demonstrate that no insulated tool spans the gap and that no
  large conductive object is in the gap.
3. The worksite must be at an elevation of 900 meters (3,000 feet) or less above sea level.

Appendix C to Subpart V of Part 1926--Protection From Hazardous
Differences in Electric Potential

I. Introduction

    Current passing through an impedance impresses voltage across
that impedance. Even conductors have some, albeit low, value of
impedance. Therefore, if a ``grounded'' \1\ object, such as a crane
or deenergized and grounded power line, results in a ground fault on
a power line, voltage is impressed on that grounded object. The
voltage impressed on the grounded object depends largely on the
voltage on the line, on the impedance of the faulted conductor, and
on the impedance to ``true,'' or ``absolute,'' ground represented by
the object. If the impedance of the object causing the fault is
relatively large, the voltage impressed on the object is essentially
the phase-to-ground system voltage. However, even faults to grounded
power lines or to well grounded transmission towers or substation
structures (which have relatively low values of impedance to ground)
can result in hazardous voltages.\2\ In all cases, the degree of the
hazard depends on the magnitude of the current through the employee
and the time of exposure. This appendix discusses methods of
protecting workers against the possibility that grounded objects,
such as cranes and other mechanical equipment, will contact
energized power lines and that deenergized and grounded power lines
will become accidentally energized.
---------------------------------------------------------------------------

    \1\ This appendix generally uses the term ``grounded'' only with
respect to grounding that the employer intentionally installs, for
example, the grounding an employer installs on a deenergized
conductor. However, in this case, the term ``grounded'' means
connected to earth, regardless of whether or not that connection is
intentional.
    \2\ Thus, grounding systems for transmission towers and
substation structures should be designed to minimize the step and
touch potentials involved.
---------------------------------------------------------------------------

II. Voltage-Gradient Distribution

    A. Voltage-gradient distribution curve. Absolute, or true,
ground serves as a reference and always has a voltage of 0 volts
above ground potential. Because there is an impedance between a
grounding electrode and absolute ground, there will be a voltage
difference between the grounding electrode and absolute ground under
ground-fault conditions. Voltage dissipates from the grounding
electrode (or from the grounding point) and creates a ground
potential gradient. The voltage decreases rapidly with increasing
distance from the grounding electrode. A voltage drop associated
with this dissipation of voltage is a ground potential. Figure 1 is
a typical voltage-gradient distribution curve (assuming a uniform
soil texture).
BILLING CODE 4510-26-P

[GRAPHIC] [TIFF OMITTED] TR11AP14.041

BILLING CODE 4510-26-C
    B. Step and touch potentials. Figure 1 also shows that workers
are at risk from step and touch potentials. Step potential is the
voltage between the feet of a person standing near an energized
grounded object (the electrode). In Figure 1, the step potential is
equal to the difference in voltage between two points at different
distances from the electrode (where the points represent the
location of each foot in relation to the electrode). A person could
be at risk of injury during a fault simply by standing near the
object.
    Touch potential is the voltage between the energized grounded
object (again, the

electrode) and the feet of a person in contact with the object. In
Figure 1, the touch potential is equal to the difference in voltage
between the electrode (which is at a distance of 0 meters) and a
point some distance away from the electrode (where the point
represents the location of the feet of the person in contact with
the object). The touch potential could be nearly the full voltage
across the grounded object if that object is grounded at a point
remote from the place where the person is in contact with it. For
example, a crane grounded to the system neutral and that contacts an
energized line would expose any person in contact with the crane or
its uninsulated load line to a touch potential nearly equal to the
full fault voltage.
    Figure 2 illustrates step and touch potentials.
BILLING CODE 4510-26-P
[GRAPHIC] [TIFF OMITTED] TR11AP14.042

BILLING CODE 4510-26-C

III. Protecting Workers From Hazardous Differences in Electrical
Potential

    A. Definitions. The following definitions apply to section III
of this appendix:
    Bond. The electrical interconnection of conductive parts
designed to maintain a common electric potential.
    Bonding cable (bonding jumper). A cable connected to two
conductive parts to bond the parts together.
    Cluster bar. A terminal temporarily attached to a structure that
provides a means for the attachment and bonding of grounding and
bonding cables to the structure.
    Ground. A conducting connection between an electric circuit or
equipment and the earth, or to some conducting body that serves in
place of the earth.
    Grounding cable (grounding jumper). A cable connected between a
deenergized part

and ground. Note that grounding cables carry fault current and
bonding cables generally do not. A cable that bonds two conductive
parts but carries substantial fault current (for example, a jumper
connected between one phase and a grounded phase) is a grounding
cable.
    Ground mat (grounding grid). A temporarily or permanently
installed metallic mat or grating that establishes an equipotential
surface and provides connection points for attaching grounds.
    B. Analyzing the hazard. The employer can use an engineering
analysis of the power system under fault conditions to determine
whether hazardous step and touch voltages will develop. The analysis
should determine the voltage on all conductive objects in the work
area and the amount of time the voltage will be present. Based on
the this analysis, the employer can select appropriate measures and
protective equipment, including the measures and protective
equipment outlined in Section III of this appendix, to protect each
employee from hazardous differences in electric potential. For
example, from the analysis, the employer will know the voltage
remaining on conductive objects after employees install bonding and
grounding equipment and will be able to select insulating equipment
with an appropriate rating, as described in paragraph III.C.2 of
this appendix.
    C. Protecting workers on the ground. The employer may use
several methods, including equipotential zones, insulating
equipment, and restricted work areas, to protect employees on the
ground from hazardous differences in electrical potential.
    1. An equipotential zone will protect workers within it from
hazardous step and touch potentials. (See Figure 3.) Equipotential
zones will not, however, protect employees located either wholly or
partially outside the protected area. The employer can establish an
equipotential zone for workers on the ground, with respect to a
grounded object, through the use of a metal mat connected to the
grounded object. The employer can use a grounding grid to equalize
the voltage within the grid or bond conductive objects in the
immediate work area to minimize the potential between the objects
and between each object and ground. (Bonding an object outside the
work area can increase the touch potential to that object, however.)
Section III.D of this appendix discusses equipotential zones for
employees working on deenergized and grounded power lines.
    2. Insulating equipment, such as rubber gloves, can protect
employees handling grounded equipment and conductors from hazardous
touch potentials. The insulating equipment must be rated for the
highest voltage that can be impressed on the grounded objects under
fault conditions (rather than for the full system voltage).
    3. Restricting employees from areas where hazardous step or
touch potentials could arise can protect employees not directly
involved in performing the operation. The employer must ensure that
employees on the ground in the vicinity of transmission structures
are at a distance where step voltages would be insufficient to cause
injury. Employees must not handle grounded conductors or equipment
likely to become energized to hazardous voltages unless the
employees are within an equipotential zone or protected by
insulating equipment.
BILLING CODE 4510-26-P

[GRAPHIC] [TIFF OMITTED] TR11AP14.043

BILLING CODE 4510-26-C
    D. Protecting employees working on deenergized and grounded
power lines. This Section III.D of Appendix C establishes guidelines
to help employers comply with requirements in Sec.  1926.962 for
using protective grounding to protect employees working on
deenergized power lines. Section 1926.962 applies to grounding of
transmission and distribution lines and equipment for the purpose of
protecting workers. Paragraph (c) of Sec.  1926.962 requires
temporary protective grounds to be placed at such locations and
arranged in such a manner that the employer can demonstrate will
prevent exposure of each employee to hazardous differences in
electric potential.\3\ Sections III.D.1 and III.D.2 of this appendix
provide guidelines that employers can use in making the
demonstration required by Sec.  1926.962(c). Section III.D.1 of this
appendix provides guidelines on how the employer can determine
whether particular grounding practices expose employees to hazardous
differences in electric potential. Section III.D.2 of this appendix
describes grounding methods that the employer can use in lieu of an
engineering analysis to make the demonstration required by Sec.
1926.962(c). The Occupational Safety and Health Administration will
consider employers that comply with the criteria in this appendix as
meeting Sec.  1926.962(c).
---------------------------------------------------------------------------

    \3\ The protective grounding required by Sec.  1926.962 limits
to safe values the potential differences between accessible objects
in each employee's work environment. Ideally, a protective grounding
system would create a true equipotential zone in which every point
is at the same electric potential. In practice, current passing
through the grounding and bonding elements creates potential
differences. If these potential differences are hazardous, the
employer may not treat the zone as an equipotential zone.
---------------------------------------------------------------------------

    Finally, Section III.D.3 of this appendix discusses other safety
considerations that will help the employer comply with other
requirements in Sec.  1926.962. Following these guidelines will
protect workers from hazards that can occur when a deenergized and
grounded line becomes energized.
    1. Determining safe body current limits. This Section III.D.1 of
Appendix C provides guidelines on how an employer can determine
whether any differences in electric potential to which workers could
be exposed are hazardous as part of the demonstration required by
Sec.  1926.962(c).
    Institute of Electrical and Electronic Engineers (IEEE) Standard
1048-2003, IEEE

Guide for Protective Grounding of Power Lines, provides the
following equation for determining the threshold of ventricular
fibrillation when the duration of the electric shock is limited:
[GRAPHIC] [TIFF OMITTED] TR11AP14.044

where I is the current through the worker's body, and t is the
duration of the current in seconds. This equation represents the
ventricular fibrillation threshold for 95.5 percent of the adult
population with a mass of 50 kilograms (110 pounds) or more. The
equation is valid for current durations between 0.0083 to 3.0
seconds.
    To use this equation to set safe voltage limits in an
equipotential zone around the worker, the employer will need to
assume a value for the resistance of the worker's body. IEEE Std
1048-2003 states that ``total body resistance is usually taken as
1000 [Omega] for determining . . . body current limits.'' However,
employers should be aware that the impedance of a worker's body can
be substantially less than that value. For instance, IEEE Std 1048-
2003 reports a minimum hand-to-hand resistance of 610 ohms and an
internal body resistance of 500 ohms. The internal resistance of the
body better represents the minimum resistance of a worker's body
when the skin resistance drops near zero, which occurs, for example,
when there are breaks in the worker's skin, for instance, from cuts
or from blisters formed as a result of the current from an electric
shock, or when the worker is wet at the points of contact.
    Employers may use the IEEE Std 1048-2003 equation to determine
safe body current limits only if the employer protects workers from
hazards associated with involuntary muscle reactions from electric
shock (for example, the hazard to a worker from falling as a result
of an electric shock). Moreover, the equation applies only when the
duration of the electric shock is limited. If the precautions the
employer takes, including those required by applicable standards, do
not adequately protect employees from hazards associated with
involuntary reactions from electric shock, a hazard exists if the
induced voltage is sufficient to pass a current of 1 milliampere
through a 500-ohm resistor. (The 500-ohm resistor represents the
resistance of an employee. The 1-milliampere current is the
threshold of perception.) Finally, if the employer protects
employees from injury due to involuntary reactions from electric
shock, but the duration of the electric shock is unlimited (that is,
when the fault current at the work location will be insufficient to
trip the devices protecting the circuit), a hazard exists if the
resultant current would be more than 6 milliamperes (the recognized
let-go threshold for workers \4\).
---------------------------------------------------------------------------

    \4\ Electric current passing through the body has varying
effects depending on the amount of the current. At the let-go
threshold, the current overrides a person's control over his or her
muscles. At that level, an employee grasping an object will not be
able to let go of the object. The let-go threshold varies from
person to person; however, the recognized value for workers is 6
milliamperes.
---------------------------------------------------------------------------

    2. Acceptable methods of grounding for employers that do not
perform an engineering determination. The grounding methods
presented in this section of this appendix ensure that differences
in electric potential are as low as possible and, therefore, meet
Sec.  1926.962(c) without an engineering determination of the
potential differences. These methods follow two principles: (i) The
grounding method must ensure that the circuit opens in the fastest
available clearing time, and (ii) the grounding method must ensure
that the potential differences between conductive objects in the
employee's work area are as low as possible.
    Paragraph (c) of Sec.  1926.962 does not require grounding
methods to meet the criteria embodied in these principles. Instead,
the paragraph requires that protective grounds be ``placed at such
locations and arranged in such a manner that the employer can
demonstrate will prevent exposure of each employee to hazardous
differences in electric potential.'' However, when the employer's
grounding practices do not follow these two principles, the employer
will need to perform an engineering analysis to make the
demonstration required by Sec.  1926.962(c).
    i. Ensuring that the circuit opens in the fastest available
clearing time. Generally, the higher the fault current, the shorter
the clearing times for the same type of fault. Therefore, to ensure
the fastest available clearing time, the grounding method must
maximize the fault current with a low impedance connection to
ground. The employer accomplishes this objective by grounding the
circuit conductors to the best ground available at the worksite.
Thus, the employer must ground to a grounded system neutral
conductor, if one is present. A grounded system neutral has a direct
connection to the system ground at the source, resulting in an
extremely low impedance to ground. In a substation, the employer may
instead ground to the substation grid, which also has an extremely
low impedance to the system ground and, typically, is connected to a
grounded system neutral when one is present. Remote system grounds,
such as pole and tower grounds, have a higher impedance to the
system ground than grounded system neutrals and substation grounding
grids; however, the employer may use a remote ground when lower
impedance grounds are not available. In the absence of a grounded
system neutral, substation grid, and remote ground, the employer may
use a temporary driven ground at the worksite.
    In addition, if employees are working on a three-phase system,
the grounding method must short circuit all three phases. Short
circuiting all phases will ensure faster clearing and lower the
current through the grounding cable connecting the deenergized line
to ground, thereby lowering the voltage across that cable. The short
circuit need not be at the worksite; however, the employer must
treat any conductor that is not grounded at the worksite as
energized because the ungrounded conductors will be energized at
fault voltage during a fault.
    ii. Ensuring that the potential differences between conductive
objects in the employee's work area are as low as possible. To
achieve as low a voltage as possible across any two conductive
objects in the work area, the employer must bond all conductive
objects in the work area. This section of this appendix discusses
how to create a zone that minimizes differences in electric
potential between conductive objects in the work area.
    The employer must use bonding cables to bond conductive objects,
except for metallic objects bonded through metal-to-metal contact.
The employer must ensure that metal-to-metal contacts are tight and
free of contamination, such as oxidation, that can increase the
impedance across the connection. For example, a bolted connection
between metal lattice tower members is acceptable if the connection
is tight and free of corrosion and other contamination. Figure 4
shows how to create an equipotential zone for metal lattice towers.
    Wood poles are conductive objects. The poles can absorb moisture
and conduct electricity, particularly at distribution and
transmission voltages. Consequently, the employer must either: (1)
Provide a conductive platform, bonded to a grounding cable, on which
the worker stands or (2) use cluster bars to bond wood poles to the
grounding cable. The employer must ensure that employees install the
cluster bar below, and close to, the worker's feet. The inner
portion of the wood pole is more conductive than the outer shell, so
it is important that the cluster bar be in conductive contact with a
metal spike or nail that penetrates the wood to a depth greater than
or equal to the depth the worker's climbing gaffs will penetrate the
wood. For example, the employer could mount the cluster bar on a
bare pole ground wire fastened to the pole with nails or staples
that penetrate to the required depth. Alternatively, the employer
may temporarily nail a conductive strap to the pole and connect the
strap to the cluster bar. Figure 5 shows how to create an
equipotential zone for wood poles.
BILLING CODE 4510-26-P

[GRAPHIC] [TIFF OMITTED] TR11AP14.045

[GRAPHIC] [TIFF OMITTED] TR11AP14.046

BILLING CODE 4510-26-C
    For underground systems, employers commonly install grounds at
the points of disconnection of the underground cables. These
grounding points are typically remote from the manhole or
underground vault where employees will be working on the cable.
Workers in contact with a cable grounded at a remote location can
experience hazardous potential differences if the cable becomes
energized or if a fault occurs on a different, but nearby, energized
cable. The fault current causes potential gradients in the earth,
and a potential difference will exist between the earth where the
worker is standing and the earth where the cable is grounded.
Consequently, to create an equipotential zone for the worker, the
employer must provide a means of connecting the deenergized cable to
ground at the worksite by having the worker stand on a conductive
mat bonded to the deenergized cable. If the cable is cut, the
employer must install a bond across the opening in the cable or
install one bond on each side of the opening to ensure that the
separate cable ends are at the same potential. The employer must
protect the worker from any hazardous differences in potential any
time there is no bond between the mat and the cable (for example,
before the worker installs the bonds).
    3. Other safety-related considerations. To ensure that the
grounding system is safe and effective, the employer should also
consider the following factors: \5\
---------------------------------------------------------------------------

    \5\ This appendix only discusses factors that relate to ensuring
an equipotential zone for employees. The employer must consider
other factors in selecting a grounding system that is capable of
conducting the maximum fault current that could flow at the point of
grounding for the time necessary to clear the fault, as required by
Sec.  1926.962(d)(1)(i). IEEE Std 1048-2003 contains guidelines for
selecting and installing grounding equipment that will meet Sec.
1926.962(d)(1)(i).

---------------------------------------------------------------------------

    i. Maintenance of grounding equipment. It is essential that the
employer properly maintain grounding equipment. Corrosion in the
connections between grounding cables and clamps and on the clamp
surface can increase the resistance of the cable, thereby increasing
potential differences. In addition, the surface to which a clamp
attaches, such as a conductor or tower member, must be clean and
free of corrosion and oxidation to ensure a low-resistance
connection. Cables must be free of damage that could reduce their
current-carrying capacity so that they can carry the full fault
current without failure. Each clamp must have a tight connection to
the cable to ensure a low resistance and to ensure that the clamp
does not separate from the cable during a fault.
    ii. Grounding cable length and movement. The electromagnetic
forces on grounding cables during a fault increase with increasing
cable length. These forces can cause the cable to move violently
during a fault and can be high enough to damage the cable or clamps
and cause the cable to fail. In addition, flying cables can injure
workers. Consequently, cable lengths should be as short as possible,
and grounding cables that might carry high fault current should be
in positions where the cables will not injure workers during a
fault.

Appendix D to Subpart V of Part 1926--Methods of Inspecting and Testing
Wood Poles

I. Introduction

    When employees are to perform work on a wood pole, it is
important to determine the condition of the pole before employees
climb it. The weight of the employee, the weight of equipment to be
installed, and other working stresses (such as the removal or
retensioning of conductors) can lead to the failure of a defective
pole or a pole that is not designed to handle the additional
stresses.\1\ For these reasons, it is essential that, before an
employee climbs a wood pole, the employer ascertain that the pole is
capable of sustaining the stresses of the work. The determination
that the pole is capable of sustaining these stresses includes an
inspection of the condition of the pole.
---------------------------------------------------------------------------

    \1\ A properly guyed pole in good condition should, at a
minimum, be able to handle the weight of an employee climbing it.
---------------------------------------------------------------------------

    If the employer finds the pole to be unsafe to climb or to work
from, the employer must secure the pole so that it does not fail
while an employee is on it. The employer can secure the pole by a
line truck boom, by ropes or guys, or by lashing a new pole
alongside it. If a new one is lashed alongside the defective pole,
employees should work from the new one.

II. Inspecting Wood Poles

    A qualified employee should inspect wood poles for the following
conditions:\2\
---------------------------------------------------------------------------

    \2\ The presence of any of these conditions is an indication
that the pole may not be safe to climb or to work from. The employee
performing the inspection must be qualified to make a determination
as to whether it is safe to perform the work without taking
additional precautions.
---------------------------------------------------------------------------

    A. General condition. Buckling at the ground line or an unusual
angle with respect to the ground may indicate that the pole has
rotted or is broken.
    B. Cracks. Horizontal cracks perpendicular to the grain of the
wood may weaken the pole. Vertical cracks, although not normally
considered to be a sign of a defective pole, can pose a hazard to
the climber, and the employee should keep his or her gaffs away from
them while climbing.
    C. Holes. Hollow spots and woodpecker holes can reduce the
strength of a wood pole.
    D. Shell rot and decay. Rotting and decay are cutout hazards and
possible indications of the age and internal condition of the pole.
    E. Knots. One large knot or several smaller ones at the same
height on the pole may be evidence of a weak point on the pole.
    F. Depth of setting. Evidence of the existence of a former
ground line substantially above the existing ground level may be an
indication that the pole is no longer buried to a sufficient depth.
    G. Soil conditions. Soft, wet, or loose soil around the base of
the pole may indicate that the pole will not support any change in
stress.
    H. Burn marks. Burning from transformer failures or conductor
faults could damage the pole so that it cannot withstand changes in
mechanical stress.

III. Testing Wood Poles

    The following tests, which are from Sec.  1910.268(n)(3) of this
chapter, are acceptable methods of testing wood poles:
    A. Hammer test. Rap the pole sharply with a hammer weighing
about 1.4 kg (3 pounds), starting near the ground line and
continuing upwards circumferentially around the pole to a height of
approximately 1.8 meters (6 feet). The hammer will produce a clear
sound and rebound sharply when striking sound wood. Decay pockets
will be indicated by a dull sound or a less pronounced hammer
rebound. Also, prod the pole as near the ground line as possible
using a pole prod or a screwdriver with a blade at least 127
millimeters (5 inches) long. If substantial decay is present, the
pole is unsafe.
    B. Rocking test. Apply a horizontal force to the pole and
attempt to rock it back and forth in a direction perpendicular to
the line. Exercise caution to avoid causing power lines to swing
together. Apply the force to the pole either by pushing it with a
pike pole or pulling the pole with a rope. If the pole cracks during
the test, it is unsafe.

Appendix E to Subpart V of Part 1926--Protection From Flames and
Electric Arcs

I. Introduction

    Paragraph (g) of Sec.  1926.960 addresses protecting employees
from flames and electric arcs. This paragraph requires employers to:
(1) Assess the workplace for flame and electric-arc hazards
(paragraph (g)(1)); (2) estimate the available heat energy from
electric arcs to which employees would be exposed (paragraph
(g)(2)); (3) ensure that employees wear clothing that will not melt,
or ignite and continue to burn, when exposed to flames or the
estimated heat energy (paragraph (g)(3)); and (4) ensure that
employees wear flame-resistant clothing \1\ and protective clothing
and other protective equipment that has an arc rating greater than
or equal to the available heat energy under certain conditions
(paragraphs (g)(4) and (g)(5)). This appendix contains information
to help employers estimate available heat energy as required by
Sec.  1926.960(g)(2), select protective clothing and other
protective equipment with an arc rating suitable for the available
heat energy as required by Sec.  1926.960(g)(5), and ensure that
employees do not wear flammable clothing that could lead to burn
injury as addressed by Sec. Sec.  1926.960(g)(3) and (g)(4).
---------------------------------------------------------------------------

    \1\ Flame-resistant clothing includes clothing that is
inherently flame resistant and clothing chemically treated with a
flame retardant. (See ASTM F1506-10a, Standard Performance
Specification for Flame Resistant Textile Materials for Wearing
Apparel for Use by Electrical Workers Exposed to Momentary Electric
Arc and Related Thermal Hazards, and ASTM F1891-12 Standard
Specification for Arc and Flame Resistant Rainwear.)
---------------------------------------------------------------------------

II. Assessing the Workplace for Flame and Electric-Arc Hazards

    Paragraph (g)(1) of Sec.  1926.960 requires the employer to
assess the workplace to identify employees exposed to hazards from
flames or from electric arcs. This provision ensures that the
employer evaluates employee exposure to flames and electric arcs so
that employees who face such exposures receive the required
protection. The employer must conduct an assessment for each
employee who performs work on or near exposed, energized parts of
electric circuits.

A. Assessment Guidelines

    Sources electric arcs. Consider possible sources of electric
arcs, including:
     Energized circuit parts not guarded or insulated,
     Switching devices that produce electric arcs in normal
operation,
     Sliding parts that could fault during operation (for
example, rack-mounted circuit breakers), and
     Energized electric equipment that could fail (for
example, electric equipment with damaged insulation or with evidence
of arcing or overheating).
    Exposure to flames. Identify employees exposed to hazards from
flames. Factors to consider include:
     The proximity of employees to open flames, and
     For flammable material in the work area, whether there
is a reasonable likelihood that an electric arc or an open flame can
ignite the material.
    Probability that an electric arc will occur. Identify employees
exposed to electric-arc hazards. The Occupational Safety and Health
Administration will consider an employee exposed to electric-arc
hazards if there is a reasonable likelihood that an electric arc
will occur in the employee's work area, in other words, if the
probability of such an event is higher than it is for the normal
operation of enclosed equipment. Factors to consider include:
     For energized circuit parts not guarded or insulated,
whether conductive objects can

come too close to or fall onto the energized parts,
     For exposed, energized circuit parts, whether the
employee is closer to the part than the minimum approach distance
established by the employer (as permitted by Sec.
1926.960(c)(1)(iii)).
     Whether the operation of electric equipment with
sliding parts that could fault during operation is part of the
normal operation of the equipment or occurs during servicing or
maintenance, and
     For energized electric equipment, whether there is
evidence of impending failure, such as evidence of arcing or
overheating.

B. Examples

    Table 1 provides task-based examples of exposure assessments.

                                 Table 1--Example Assessments for Various Tasks
----------------------------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------------------------
                                   Task                                    Is employee exposed to flame or
                                                                            electric-arc hazard?
--------------------------------------------------------------------------
Normal operation of enclosed equipment,   The employer properly installs   No.
 such as closing or opening a switch.      and maintains enclosed
                                           equipment, and there is no
                                           evidence of impending failure.
                                          There is evidence of arcing or   Yes.
                                           overheating.
                                          Parts of the equipment are       Yes.
                                           loose or sticking, or the
                                           equipment otherwise exhibits
                                           signs of lack of maintenance.
--------------------------------------------------------------------------
Servicing electric equipment, such as racking in a circuit breaker or      Yes.
 replacing a switch.
-----------------------------------------
Inspection of electric equipment with     The employee is not holding      No.
 exposed energized parts.                  conductive objects and remains
                                           outside the minimum approach
                                           distance established by the
                                           employer.
                                          The employee is holding a        Yes.
                                           conductive object, such as a
                                           flashlight, that could fall or
                                           otherwise contact energized
                                           parts (irrespective of whether
                                           the employee maintains the
                                           minimum approach distance).
                                          The employee is closer than the  Yes.
                                           minimum approach distance
                                           established by the employer
                                           (for example, when wearing
                                           rubber insulating gloves or
                                           rubber insulating gloves and
                                           sleeves).
--------------------------------------------------------------------------
Using open flames, for example, in wiping cable splice sleeves...........  Yes.
----------------------------------------------------------------------------------------------------------------

III. Protection Against Burn Injury

A. Estimating Available Heat Energy

    Calculation methods. Paragraph (g)(2) of Sec.  1926.960 provides
that, for each employee exposed to an electric-arc hazard, the
employer must make a reasonable estimate of the heat energy to which
the employee would be exposed if an arc occurs. Table 2 lists
various methods of calculating values of available heat energy from
an electric circuit. The Occupational Safety and Health
Administration does not endorse any of these specific methods. Each
method requires the input of various parameters, such as fault
current, the expected length of the electric arc, the distance from
the arc to the employee, and the clearing time for the fault (that
is, the time the circuit protective devices take to open the circuit
and clear the fault). The employer can precisely determine some of
these parameters, such as the fault current and the clearing time,
for a given system. The employer will need to estimate other
parameters, such as the length of the arc and the distance between
the arc and the employee, because such parameters vary widely.

  Table 2--Methods of Calculating Incident Heat Energy From an Electric
                                   Arc
------------------------------------------------------------------------

-------------------------------------------------------------------------
1. Standard for Electrical Safety Requirements for Employee Workplaces,
 NFPA 70E-2012, Annex D, ``Sample Calculation of Flash Protection
 Boundary.''
2. Doughty, T.E., Neal, T.E., and Floyd II, H.L., ``Predicting Incident
 Energy to Better Manage the Electric Arc Hazard on 600 V Power
 Distribution Systems,'' Record of Conference Papers IEEE IAS 45th
 Annual Petroleum and Chemical Industry Conference, September 28--30,
 1998.
3. Guide for Performing Arc-Flash Hazard Calculations, IEEE Std 1584-
 2002, 1584a--2004 (Amendment 1 to IEEE Std 1584-2002), and 1584b-2011
 (Amendment 2: Changes to Clause 4 of IEEE Std 1584-2002).*
4. ARCPRO, a commercially available software program developed by
 Kinectrics, Toronto, ON, CA.
*This appendix refers to IEEE Std 1584-2002 with both amendments as IEEE
 Std 1584b-2011.
------------------------------------------------------------------------

    The amount of heat energy calculated by any of the methods is
approximatelyinversely proportional to the square of the distance
between the employee and the arc. In other words, if the employee is
very close to the arc, the heat energy is very high; but if the
employee is just a few more centimeters away, the heat energy drops
substantially. Thus, estimating the distance from the arc to the
employee is key to protecting employees.
    The employer must select a method of estimating incident heat
energy that provides a reasonable estimate of incident heat energy
for the exposure involved. Table 3 shows which methods provide
reasonable estimates for various exposures.

                                         Table 3--Selecting a Reasonable Incident-Energy Calculation Method \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                     600 V and Less \2\            601 V to 15 kV \2\              More than 15 kV
              Incident-energy calculation method               -----------------------------------------------------------------------------------------
                                                                 1[Phi]    3[Phi]a   3[Phi]b   1[Phi]    3[Phi]a   3[Phi]b   1[Phi]    3[Phi]a   3[Phi]b
--------------------------------------------------------------------------------------------------------------------------------------------------------
NFPA 70E-2012 Annex D (Lee equation)..........................       Y-C        Y         N        Y-C       Y-C        N     N \3\     N \3\     N \3\

Doughty, Neal, and Floyd......................................       Y-C        Y         Y         N         N         N         N         N         N
IEEE Std 1584b-2011...........................................        Y         Y         Y         Y         Y         Y         N         N         N
ARCPRO........................................................        Y         N         N         Y         N         N         Y     Y \4\     Y \4\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Key:
1[Phi]: Single-phase arc in open air
3[Phi]a: Three-phase arc in open air
3[Phi]b: Three-phase arc in an enclosure (box)
Y: Acceptable; produces a reasonable estimate of incident heat energy from this type of electric arc
N: Not acceptable; does not produce a reasonable estimate of incident heat energy from this type of electric arc
Y-C: Acceptable; produces a reasonable, but conservative, estimate of incident heat energy from this type of electric arc.
Notes:\1\ Although the Occupational Safety and Health Administration will consider these methods reasonable for enforcement purposes when employers use
  the methods in accordance with this table, employers should be aware that the listed methods do not necessarily result in estimates that will provide
  full protection from internal faults in transformers and similar equipment or from arcs in underground manholes or vaults.
\2\ At these voltages, the presumption is that the arc is three-phase unless the employer can demonstrate that only one phase is present or that the
  spacing of the phases is sufficient to prevent a multiphase arc from occurring.
\3\ Although the Occupational Safety and Health Administration will consider this method acceptable for purposes of assessing whether incident energy
  exceeds 2.0 cal/cm\2\, the results at voltages of more than 15 kilovolts are extremely conservative and unrealistic.
\4\The Occupational Safety and Health Administration will deem the results of this method reasonable when the employer adjusts them using the conversion
  factors for three-phase arcs in open air or in an enclosure, as indicated in the program's instructions.

    Selecting a reasonable distance from the employee to the arc. In
estimating available heat energy, the employer must make some
reasonable assumptions about how far the employee will be from the
electric arc. Table 4 lists reasonable distances from the employee
to the electric arc. The distances in Table 4 are consistent with
national consensus standards, such as the Institute of Electrical
and Electronic Engineers' National Electrical Safety Code, ANSI/IEEE
C2-2012, and IEEE Guide for Performing Arc-Flash Hazard
Calculations, IEEE Std 1584b-2011. The employer is free to use other
reasonable distances, but must consider equipment enclosure size and
the working distance to the employee in selecting a distance from
the employee to the arc. The Occupational Safety and Health
Administration will consider a distance reasonable when the employer
bases it on equipment size and working distance.

    Table 4--Selecting a Reasonable Distance from the Employee to the
                              Electric Arc
------------------------------------------------------------------------
                                   Single-phase arc   Three-phase arc mm
       Class of equipment            mm  (inches)           (inches)
------------------------------------------------------------------------
Cable...........................  NA*...............            455 (18)
Low voltage MCCs and panelboards  NA................            455 (18)
Low-voltage switchgear..........  NA................            610 (24)
5-kV switchgear.................  NA................            910 (36)
15-kV switchgear................  NA................            910 (36)