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Surge Protectors

A surge protector, also known as a surge strip or surge suppressor, is commonly a multi-outlet strip that offers built-in protection against overvoltage. Surge protectors do not protect against undervoltage; they protect against voltage increases. Figure 4.31 shows a picture of a surge protector.

Figure 4.31

Figure 4.31. Surge protector

Most surge protectors have an electronic component called an MOV (metal oxide varistor), which protects the computer or device that plugs into one of the outlets on the surge strip. An MOV is positioned between the AC coming in and the outlet into which devices are plugged. When a surge occurs, the MOV prevents the extra voltage from passing to the outlets. An MOV, however, has some drawbacks. If a large surge occurs, the MOV will take the hit and be destroyed, which is better than damaging the computer. However, with small overvoltages, each small surge weakens the MOV. A weakened MOV might not give the proper protection to the computer in the event of a bigger surge. Also, there is no simple check for an MOV’s condition. Some MOVs have indicator lamps attached, but they indicate only when the MOV has been destroyed, not when it is weakened. Still, having an indicator lamp is better than nothing at all. Some surge protectors also have replaceable fuses and/or indicator lamps for the fuse. A fuse works only once and then is destroyed during a surge in order to protect devices plugged into surge protector outlets.

Several surge protector features deserve consideration. Table 4.8 outlines some of them.

Table 4.8. Surge protector features



Clamping voltage

The level at which surge protector starts protecting the computer. The lower the value, the better the protection.

Clamping speed

How much time elapses before protection begins. The lower the value, the better the protection. Surge protectors cannot normally protect against power spikes (overvoltages of short duration) because of their rated clamping speed.

Energy absorption/dissipation

The greater the number of joules (a unit of energy) that can be dissipated, the more effective and durable a surge protector is. This feature is sometimes called energy absorption. A surge protector rating of 630 joules is more effective than a rating of 210 joules.

TVS (transient voltage suppressing) rating

This is also known as response time. The lower the rating the better. For example, a 330 TVS-rated surge protector is better than a 400 TVS-rated one.

UL rating

UL (Underwriters Laboratories) developed the UL 1449 VPR (voltage protection rating) standard to measure the maximum amount of voltage a surge protector will let through to the attached devices. The UL 497A standard is for phone line protection, and the UL 1283 standard is for EMI/RFI.

The federal government designates surge suppressor grades—A, B, and C. Suppressors are evaluated on a basis of 1,000 surges at a specific number of volts and amps. A Class A rating is the best and indicates tolerance up to 6,000 volts and 3,000 amps.

Surge protectors are not the best protection for a computer system because most provide very little protection against other adverse power conditions. Even the good ones protect only against overvoltage conditions. Those with the UL 1449 rating and an MOV status lamp are usually more expensive. Unfortunately, people tend to put their money into their computer parts, but not into the protection of those parts.

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