Voltage-Surge Protector

Image Gallery Depending on what equipment you need protected from voltage surge, you can employ one of three devices. One is stock; the other two are modified. ""Better"" (right in photo): Metal-oxide varistors for surge protection. ""Best"" (left in photo): Metal-oxide varistors, RF chokes, and capacitors for surge protection and filtering. Both surge protectors use MOV protection between hot and neutral lines and between both legs and ground for full isolation from transients.

Protect your sensitive electronic equipment from lightning damage by building your own ...

By TJ Byers

"Snap, crackle, pop" may be familiar breakfast sounds to some people, but for many others, such noises signal disaster ...lightning disaster.

Each year, the damage done by lightning runs into the millions of dollars, and the human casualties number in the thousands. As a matter of fact, more people are killed each year by this form of electric discharge than by all other natural disasters combined.

Lightning wreaks the most financial havoc, however, when it damages electronic equipment. Stereos, televisions, and home computers succumb to the effects of this force daily. And the most perplexing part of the problem is that lightning doesn't even have to strike an appliance directly to inflict damage. Flashes many miles away can turn hundreds or thousands of dollars' worth of circuitry into high-tech junk.

VOLTAGE SURGES

The problem comes from the utility-fed electricity used to run your equipment. The power delivered to your home has probably traveled through hundreds of miles of wire and several substations before it reaches you.

When lightning strikes, it does so with the force of millions of volts. You can actually hear lightning discharge several miles away (and I don't mean the thunder) if you listen to an AM radio during a thunderstorm. The highvoltage discharge generates radio waves that are picked up by your radio's antenna.

In a similar fashion, the sprawling utility grid can pick up static from lightning. When a strike comes close to a power line, the wires act as a large antenna and absorb part of the energy. A power surge as high as 2,500 volts can be injected into the grid in this manner. These voltage surges travel down the wires into your home and right into appliances, where they can destroy sensitive electronic parts ...even though the equipment is turned off.

Fortunately, you can protect your costly possessions from this threat without having to unplug them every time the sky clouds over. There is an electronic device called a metaloxide varistor (MOV for short) that can serve as a watchdog on the voltage of your AC line.

As long as your household voltage remains within normal limits, the MOV does nothing. Let the voltage suddenly surge to 130 or higher, though, and the MOV swings into action. What it does is absorb the extra voltage created by the spike and dissipate it as heat. When the line voltage returns to normal, the MOV goes back on standby. The entire sequence happens in about onemillionth of a second.