Choosing a Surge Suppressor
By Michael Seaforth
Most people protect their computer with a surge suppressor. So, how should someone go about choosing one? Should you just buy the most expensive one in the store? Should you assume that the $30 unit is better than the $20 one? Ultimately, there is a limit to what each of us is willing to spend on protection. By looking carefully at the specifications on the package, we can put ourselves in a better position to make a wise choice.

Suppressors are used to provide some measure of protection from sudden increases in voltage and current that could damage a computer or other electronic device. We therefore want the suppressor to operate quickly, be able to handle a lot of energy without being destroyed and keep both the voltage and current in check.

Many factors contribute to the severity of the surge that might occur at a computer. The design of the power system in the area you live and the likelihood of lightning storms are beyond your control. However, within the building, you can select the level of protection you want.

For the typical home user where the only protection available is the suppressor at the computer and where cost is an important determining factor, paying attention to certain key specifications (often in very small print) will increase the bang for the buck. A suppressor that is also equipped with modem and fax protection will offer even greater protection since surges can enter the home through the telephone line. The values shown below pertain to the power section of 120 V surge suppressors only.

Response Time: This should be less than 1 ns (nanosecond).

Clamping Voltage: This should not be greater than 330 V

Maximum Surge Energy/Dissipation: This will determine whether your suppressor survives or gives up the ghost. Pay close attention to this when comparing suppressors. The higher the value, the better. The value is expressed in Joules (J) and may vary from about 270 to 1200J or more for your typical suppressor. In severe cases a suppressor may become permanently damaged and have to be replaced after handling a powerful surge.

EMI/RMI Filtering: This is sometimes just shown as attenuation and is expressed in decibels (db). This is a measure of how well it will protect your system from power line disturbances that can cause your computer to freeze up or data on your hard drive to become corrupted. A higher number is better. Typical values range from 15 to 40 db for your home suppressor. However, unless the values shown are at the same frequency, a proper comparison cannot be made.

Maximum Surge/Spike Current: This is a measure of the ability of the unit to handle current surges without being destroyed. Usually shown in kiloamps (kA), a larger number is better.

Lastly and most importantly, you should ensure that the device is approved to the safety standards for the country you live in. Many people neglect to do this and may be putting themselves at risk. Typical markings to look for are the UL marking in the US and the CSA, cUL or other marking in Canada. Users outside of North America should enquire about the approval required for their country.

So, now that you have purchased and installed your suppressor, is your computer safe from harm? Well, it is never totally safe but there is only so much you can do without spending an arm and a leg.

CAUTION: Always make sure that the ground terminal on the plug is intact and connected at the power bar or suppressor. You should also verify that the ground terminal is also connected at the wall and that all receptacles are properly grounded. For this, you will need the help of a qualified electrician or you could purchase an inexpensive circuit tester at a hardware or electronics store. The purpose of the third terminal is to protect the user from electrical shock and to enable the suppressor to perform its intended function correctly.