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Lightning that strikes some distance from your home is still very threatening to electronics, but in such cases there is inexpensive protection available. Because both the phone and electrical companies equip their lines with lightning suppression equipment, a direct hit on a pole will largely be grounded. Only the induced voltage—generally on the order of thousands, rather than millions, of volts—is a problem. Readily available devices called surge suppressors can handle induced surges.

A surge suppressor consists of a complement of electronics usually built into a special electrical outlet. Inside, solid-state electronics such as avalanche diodes and metaloxide varistors (MOVs) lie in wait for an abnormally high voltage. The diodes and MOVs are wired across t he three legs of a standard household circuit: hot, neutral and ground. When the voltage exceeds the rating of the diodes or the MOVs (typically around 300 volts), they become conductive and allow excess voltage to shunt across the circuit before it can enter the appliance.

When you're protecting electronics in your home from lightning, don't forget equipment connected to phone lines. Lightning is just as happy to make its entrance that way as through power lines, and answering machines and computer modems are fragile pieces of equipment. Worse, the damage may not stop there. Lightning-induced voltage surges can get into a computer through the phone line and modem and proceed to destroy the main circuit board and the disk drives and then even find their way out to the monitor or printer. It's not unusual to lose everything because of one forgotten phone line. Either unplug phone lines when they're not being used, or buy surge suppressors for them.

The success of a surge protector depends on several things. First, it must be wired to serve all three legs of the circuit. The least expensive surge protectors typically have one MOV wired between hot and neutral, making them little better than useless. Second, the surge protector must be able to respond to lightning's incredibly rapid voltage rise.

Avalanche diodes are very quick but can't handle much power; MOVs are slow but stout. That's why they're often used in combination. Still, situations occasionally arise where even this team can't meet the challenge; surge suppression doesn't offer complete protection. Third, the components must be undamaged. Because the diodes and MOVs do nothing when nothing is wrong, you can't tell if they've been ruined by a prior lightning strike. Surge protectors with a circuit to indicate the integrity of the devices are best. (If you don't mind a little simple soldering, you can build an adequate surge suppressor yourself. TJ Byers described the assembly of a simple MOV-based unit in MOTHER No. 89, page 118.)

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