by Nick Gromicko and Rob London
- lightning. When lightning strikes near a power line, millions of volts of electricity can feed into a building and overload any connected appliances. The only defense against this form of power surge is to unplug sensitive appliances during storms, as typical surge protectors do not provide sufficient protection;
- the operation of high-powered electrical devices, such as vacuum cleaners, refrigerators and air conditioners. These appliances can place large and sudden demands on a building’s electrical system, upsetting the steady flow of electricity to sensitive appliances and electronics throughout the house. Even minor power spikes, if they occur regularly, can damage sensitive components in electronics throughout a building; and
- mechanical failure, such as faulty wiring or downed power lines.
Surge suppression is typically provided by one or more metal-oxide varistors (MOVs), which are two-terminal semiconductors whose function is similar to pressure-sensitive valves, by conducting electricity only when the power level reaches a threshold beyond safe fluctuations. The excess voltage is re-routed to the ground wire, safely dissipating the voltage into the earth. As the MOV only diverts the surge current while leaving the normal current to flow into the appliance, the operation of surge-protected electrical devices should not be interrupted during power spikes or surges. This same principle is employed using gas-discharge arrestors (GDAs), which use an inert gas that ionizes and becomes an effective conductor only at unsafe voltages. Surge suppression may be achieved through the use of either of these designs, which may be accompanied by backup fuses that burn out and close the circuit when excess voltage is not stopped by the surge suppressor.
Inspectors and homeowners may note a few warnings concerning MOVs and GDAs:
- They will eventually fail after repeated surges, which is why high-quality surge protectors incorporate warning lights or alarms to inform homeowners that the suppressor is no longer functional. However, lights and alarms are no guarantee of the functionality of the surge suppressor, so they should be replaced periodically to ensure the safety of sensitive electronics. Failed MOVs that are not disconnected have been known to start fires themselves.
- They will not work if the power or electrical receptacle does not have a ground wire. If the surge or spike is not sent to ground by the surge protector, it will destroy the delicate electronics they were meant to protect. The warranty offered by a surge protector's manufacturer is only valid if the surge protector is used in a properly grounded outlet.
InterNACHI inspectors may check for a sticker that identifies the unit as a transient-voltage surge suppressor. These units have met the criteria for Underwriters Laboratories (UL) 1449, the UL's minimum performance standard for surge suppressors. InterNACHI inspectors should be aware of the common misconception that surge suppressors and power strips are the same thing, as many power strips have no ability to protect against power surges. A power strip that's designed merely for use as an extension cord and which bears a sticker that labels it as a “relocatable power tap” should not be relied upon for protection during power surges.
Due to the electrical sensitivity and expense of computers, it is strongly advised that they are connected to a UL-listed surge protector, which contains the following metrics:
- clamping voltage, which is the smallest voltage that will cause the MOVs to conduct electricity to the ground wire. There are three levels of protection: 330V, 400V and 500V. Lower clamping voltages offer better protection;
- energy absorption, which is a rating in joules used to determine how much energy the suppressor can absorb before it fails. Higher numbers, such as 600 joules or more, indicate better protection; and
- response time, which indicates the amount of time that equipment will be exposed to a power surge before the suppressor kicks in. High-quality suppressors will activate in less than one nanosecond.