ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Tuesday, May 7, 1996 TAG: 9605070095
SECTION: EXTRA PAGE: 3 EDITION: METRO
COLUMN: At Home with Technology
SOURCE: DAVID BUTLER
Q: I bought a plug-in surge suppressor for my PC, but hadn't given much thought to all the other electronics I own - that is, until a voltage spike took out my programmable thermostat. Could I protect all the products in my home with a single surge protection device?
A: Here's what likely caused the demise of your thermostat: When a motor or compressor shuts off, the magnetic field that turns the armature suddenly collapses. During this brief instant, the motor acts as a generator, producing a very large voltage spike. Air conditioning compressors generate surges that can reach several thousand volts!
Prior to microelectronics, voltage surges were of little concern to most of us. Low-tech appliances, including "pre-electronic" telephones and televisions, could tolerate all but the most severe spikes. Now that microprocessors are running everything from dishwashers to vacuum cleaners, damage from voltage surges and other electrical system anomalies is on the rise.
Lightning is by far the most dangerous source of voltage surges. It often propagates along power transmission lines, extending its effect well beyond the actual strike location - sometimes farther than you can hear the thunder. Transmission line surges can also be caused by cloud-to-cloud lightning. (This happens through a process known as induction.)
Compared to lightning, mechanically induced surges are downright boring. Nonetheless, mechanical surges are far more frequent than indirect lightning and can be just as damaging. For example, a brief but powerful spike rings through electrical distribution lines as power returns after an interruption. Unfortunately, damage is not always obvious - in some cases, the effects can be incremental.
One of the worst scenarios is when the power flickers or turns off and on repeatedly. This extreme form of short cycling is especially hard on compressors. Although most digital thermostats and refrigerators include a "time-out" circuit to prevent short cycling, this does nothing to shield from the barrage of voltage spikes.
No doubt, some products are built better than others when it comes to fault-tolerance. However, given the reality of space and cost constraints, there's not much a product designer can do to defend against large electrical surges. Likewise, it would not be practical for a consumer to purchase dedicated surge protection devices for every product in the home.
Whole-house surge suppression offers a practical alternative. In fact, it's the only way to protect hard-wired products such as a thermostat. The suppressor connects to the electrical system at the main breaker panel. Some models are small enough to fit inside the panel while others mount adjacent to the panel. Professional installation is required.
A whole-house suppressor can adequately protect most appliances as well as the electrical system itself (wiring, fixtures and breakers). However, sensitive electronics such as a personal computer or home theater system still needs the superior protection of a point-of-use surge suppressor. This is especially true of products that connect to both the power line and the telephone or cable network.
A surge suppressor is only as good as its path to ground. Unfortunately, many homes are inadequately grounded. Whether you rely on point-of-use or whole-house protection or both, it's imperative to provide a low-resistance path to ground. Problems are often the result of poor soil quality or loose or corroded connections. In some locales, two grounding rods are mandatory. More is better.
Hopefully, whole-house surge protection will someday become a standard feature on all homes. For now, consumers are left to fend for themselves or suffer the consequences.
To receive a list of companies that manufacture whole-house and point-of-use surge protection products, please send $1.50 and a self-addressed envelope to David Butler F-611, Department TWN, 14713 Pleasant Hill Road, Charlotte, N.C. 28278-7927. The list includes toll-free phone numbers, selection tips and a features comparison chart.
Tech Talk
There are two types of whole-house surge protection devices: transient voltage surge suppressors (TVSS) and secondary surge arresters (aka lightning arresters). The later is a simple device, intended primarily to short the electrical system to ground in case of a catastrophic surge. A TVSS is more sophisticated, acting continuously to clip the peaks from all surges that exceed a specified "clamping" voltage (typically 330 or 400 volts).
LENGTH: Medium: 86 lines ILLUSTRATION: GRAPHIC: A whole-house device, backed by a good groundingby CNBsystem, will adequately shield most products from damaging surges.