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Introduction
Surge Protection
The generic term Surge Protection covers a number of product names.

Some of the are:

Surge Filters
Surge Diverters
Power Protectors
Surge Busters
Power Filters
Spike Filters.

There are really only two types of units you should consider buying:

  1. Series Power Filter. Best Quality Heavy Duty
A series power filter is connected in line/series with your equipment so it has the total amount of load current flowing through the device, so if you equipment you want to protect is rated at 15 amps then you need a 15 amp series power filter.
They will filter out electrical noise, normal mode -- active to neutral and common mode -- active/neutral to earth.
If the filter you are about to buy does not have have a current rating per se, then it is not a series power filter, no matter what the salesman says.

  1. Shunt Surge Diverter. Light Duty.
A shunt power filter is connected across the line/parallel with your equipment.
There are no current ratings on the device.
They are basically a voltage dependant resistor, known as a MOV, metal oxide varistor, so when the voltage rises above a certain level say 270 volts they will start to conduct the higher voltage to ground.
Most UPS systems and computer power supplies have a form of surge diverter connected across thier input terminals, this is why they sometimes trip out earth leakage circuit breakers[ safety switches]