A surge protector is an device placed in the circuit between the power source and electrical devices and designed to protect electrical devices from voltage spikes. A surge protector attempts to regulate the voltage supplied to an electric device by either blocking or by shorting to ground voltages above a safe threshold. Note that a surge protector is usually in the form of a power strip with or without the extension cord. However, a power strips may not be a surge protector for it may lack of the surge protection circuit.
The most important specifications of a surge protector for AC mains, as well as some communication protection, include:
- Clamping voltage (let-through voltage) - A lower clamping voltage indicates better protection, but a shorter life expectancy. The standard let-through voltage for 120 V AC devices is 330 volts.
- Joules – This number defines how much energy the surge protector can absorb without failure. A higher number indicates longer life expectancy because the device will divert more energy elsewhere and will absorb less energy. Better protectors exceed 1000 joules and 40,000 amperes.
- Response time – The longer the response time the longer the connected equipment will be exposed to the surge. Typical surges usually take a few microseconds to reach their peak voltage and a surge protector with a nanosecond response time would kick in fast enough to suppress the most damaging portion of the spike.
- Standards – The surge protector may meet IEC 61643-1, EN 61643-11 and 21 , Telcordia Technologies Technical Reference TR-NWT-001011, ANSI / IEEE C62.xx, or UL1449.
The principal components used in a surge protection circuit may include some of the followings:
- Metal oxide varistor
- Transient suppression diode
- Gas discharge tube (GDT)
- A selenium voltage suppressor
- A quarter-wave coaxial surge arrestor
- Carbon block spark gap overvoltage suppressor
- Series Mode (SM) surge suppressors