(16) The factor oi safety for the poles shall be calculated at 10 for a wind
pressure of 25 lbs. per square foot, the effective area of a round pole being taken
at '6 of the mean diameter of the exposed part into the length of that part.
Steel Poles.
(17) Poles of tubular type shall be painted with oil paint not less than once
every five years, and poles of lattice type not less than once every three years.
(18) Each pole shall be set in concrete.
(19) The concrete below the pole shall be dropped on to a substantial cast-
iron earth plate bonded to the pole by a wire or rod.
(20) The factor of safety of the pole shall be not less than 6 taking the
maximum wind pressure at 25 lbs. per square foot. In the case of lattice poles
the pressure on the lee side will be taken as one half of the pressure on the wind-
ward side.
Arms.
(21) The conductors shall be carried on insulators mounted singly, or in
pairs on steel channel arms, or singly upon iron brackets fastened to the poles ;
or, if wooden arms are used, an earthing strip or stout wire shall be fastened on
the upper side of each arm.
Road Crossings.
(22) Where the line crosses over a public road, canal, or railway, the angle
between the Hne and the direction of the road, canal, 'or railway at the place of
crossing shall not be less than 60° and the height of the line not less than 25 feet.
