Power Filters

The mains power in Australia is a 220/240 volt alternating current supply.

This power theoretically should be a pure sine wave. (Diagram 1)

In reality it is often affected by spikes and surges which corrupt the wave form. (Diagram 2) 

Diagram 1	Diagram 2

These spikes and surges can be caused by powering on or off devices such as air conditioners, motors, welders, industrial machines etc. Industrial areas because of machinery and commercial premises because of air conditioning systems are most at risk. Residential areas are not immune to power problems however.

These spikes (very short duration but high voltage) and surges (higher than normal voltage levels) can and do damage electronic equipment. A large spike may cause an immediate failure, but many smaller spikes will cause cumulative damage.

Power filters reduce the likelihood of these surges and spikes reaching the equipment connected to them.

A good quality power filter will have multi-stage circuitry giving better protection than the cheaper simple, single stage filters.

Data corruption may also be caused by a poorly filtered mains power supply, so preventing physical damage to the equipment is not the sole benefit of these devices.

An unusually large spike or surge may damage the power filter, so that it no longer protects the equipment connected to it. Typically when this happens the power still flows to any equipment connected, but it is no longer protected.

A good quality power filter will have an indicator to show that the device is protecting the equipment connected to it. This is usually a light that goes out when the filter has failed. Don’t buy a power filter without this feature and check the indicator regularly.

Additional features may include telephone line or network cable protection. If you use a modem, make sure your power filter has this feature. A spike down the telephone line can destroy a computer that is otherwise protected by a power filter.

All connected computer equipment should be protected by a power filter as shown below.

A power surge or spike can cause damage when equipment is not properly installed as shown below.
The printer is not protected by a power filter and a power spike could enter the printer via the power cable then travel through the data cable and damage the computer.