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Surge Protection

Most of our readers know to plug their computer equipment into a surge protector, but not everyone can tell an excellent unit from a poor one. Using a poor one is only slightly better than none at all and leaves you with a false sense of security. The first time the surge suppressor is really needed that false sense of security will get blown away, along with some expensive electronics.

Although a majority of power surges will be caused by electrical equipment in use on your property or in the local area, the most serious threat comes from lightning. Most computers and other electronic appliances are designed to withstand a surge of about 300-400 volts. A lightning bolt hitting the nearest power transformer can easily send an instant spike of 10,000 volts down the AC wiring, and if your surge suppressor isn’t up to the task, that new computer system is toast.

There are several methods used by surge suppressors, no one of which is entirely satisfactory by itself. A good surge suppressor will use a combination of these methods:

1. Absorption – The protected line is clamped, or limited to a peak voltage, and everything over that is shunted into a circuit that will absorb it. Effectiveness is limited by the clamping speed and the amount of energy that can be absorbed.

2. Filtering – Isolated surges are filtered out, usually by using an inductor (coil) in series with the line. The inductor will impede sudden changes in voltage but provides no protection if the voltage goes up and stays up for more than a few milliseconds.

3. Diversion – This is similar to absorption except that instead of being absorbed, the excess is diverted to the ground leg of the AC line.

An important component of the suppressor unit is a metal oxide varistor (MOV). These devices are good at clamping surges of 300 volts or more, but are most effective when used in combination with circuitry for filtering and diversion or absorption.

The filtering capability of a surge suppressor is rated in joules. This is a measure of energy, and you might think of it as how big a punch the unit can withstand. Most cheap surge suppressors are rated at less than 500 joules. We recommend a rating of at least 1000 joules.

Here are some other features to look for in a good power surge protector:

1. Let-through voltage. This should be 300 volts or less.

2. Building wiring fault indicator. No surge suppressor will be as effective if the outlet is not grounded or the AC is improperly phased. This indicator will give you a heads-up for those conditions.

3. Protection function indicator. This tells you that the surge unit itself is working properly. If it’s not, replace it. These are not field-reparable.

4. Fast-acting thermal fuse. No unit in my budget or yours will absorb a direct lightning strike. The best defense for that is to sacrifice a fuse and open the line completely.

5. Phone-line surge protection. Phones are cheaper than computers, but the phone line is also vulnerable to surges and should be protected, for personal safety if nothing else. This feature is easily recognized by a pair of RJ-11 jacks.

6. Coax TV cable protection. Whether you get a TV signal from the cable company or a rooftop antenna, it’s another avenue for lightning surges to get in. If you use rabbit ears, you can safely ignore this one.

Disclaimer - The Micro 2000 Tech Tip is a free service providing information only. While we use reasonable care to see that this information is correct, we do not guarantee it for accuracy, completeness or fitness for a particular purpose. Micro 2000, Inc. shall not be liable for damages of any kind in connection with the use or misuse of this information.