Protecting your electrical appliances

The reality is that power interruptions will occur - whether planned or unplanned. Even if you only have one interruption in a year, you need to consider the impact this could have on your home and develop an appropriate plan. This could be as simple as having a torch in the cupboard, or as sophisticated as fitting an uninterruptible power supply (UPS).

Surge Diverters

Surge Diverters restrict incoming voltages to predetermined levels, directing the associated fault current to earth. The earth connection of the diverter must be sound and of low resistance to ensure it provides adequate protection. If not properly selected and installed for the magnitude of the surge expected, they may be destroyed by the energy which passes through them when they operate.

These devices minimise the effect of rapid voltage increases above a design threshold voltage but do not provide protection against prolonged voltage decreases or momentary interruptions. These are generally used to protect against lightening striking overhead lines.

Power Filters

Power filters minimise the effect of rapid voltage surges but do not provide protection against prolonged voltage sags or momentary interruptions. Power filters can also remove or attenuate electrical noise that can interfere with the operation of equipment.

Line Conditioners

Line conditioners filter out voltage fluctuations and also provide a constant voltage output over a wide range of input voltages. They can also, in many cases, prevent disturbances from the equipment they are protecting being transferred to the rest of the system.

Line conditioners are not able to protect against prolonged power interruptions because they do not incorporate an energy source. The extent to which a line conditioner can cope with voltage fluctuations depends on its design and the demands placed upon it.

Stand-by Power Supplies

Stand-by power supplies are normally off-line but come on-line as soon as the voltage drops below a pre-set level. The stand-by supply is usually provided by a battery in which case the power supply will incorporate a battery charger and an inverter to convert the DC battery power back into an AC output.

There will be a small but significant delay while the load is transferred to the stand-by supply and the equipment being protected must be able to tolerate the brief loss of supply.

It may be necessary to incorporate a line conditioner at the input to your equipment to protect against electrical noise and voltage transients, and also against voltage sags that are not of sufficient magnitude to cause the stand-by power supply to operate but which may have an adverse effect on the equipment being protected.

Uninterruptible Power Supply

An uninterruptible power supply (UPS) provides protection against supply interruptions as well as against voltage variations. Uninterruptible power supplies are in constant operation and incorporate an energy source such as batteries and an inverter through which the equipment being protected is supplied. In the event of loss of mains power, the batteries maintain a continuous supply to the protected equipment for a period of time. The capacity of the UPS needs to be matched to your requirements for the length of time you want to maintain supply: in many cases you may decide that you only need sufficient time to save data and shut down the equipment in a controlled fashion.

The uninterruptible power supply can be used in conjunction with a stand-by generator to provide power for extended outages beyond the capacity of the UPS's internal battery.

(Source: ESAA Customer Guide to Electricity Supply)