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Lightning Safety

Surge Arrestors for Lightning and EMP Protection

Mick Abraham

©1996 Mick Abraham The numerous Home Power articles

on system grounding point out the

importance of lightning protection. Certain environmental and climatic conditions seem to indicate that lightning activity is on the increase.

Home power systems are particularly vulnerable to lightning surges. Racks, trackers, and wind towers sometimes think they are lightning rods. Solar arrays with numerous interconnections provide a large capture area for surge energy. The result can be dangerously high voltages and static charges in the system.

You may have seen the “spice bottle” sized surge protectors at the local electronics store. These consumer-grade units are low priced, but there is a whole world of industrial-grade protectors that you’ll never find in a blister pack. Power companies, the military, and TV and radio stations demand high performing spike arrestors and grounding systems. Industry has responded, and with a little ingenuity, home power systems can achieve similar levels of protection.

Shunt Protection

There are two basic kinds of surge arrestors. Shunting type protectors don’t do anything until a surge occurs. When they sense excessive voltage they momentarily switch the spiked line(s) to a direct or indirect earth ground. The turn-on voltage for a particular suppressor must be specified when you order it.

Shunting protectors tend to share part of the surge with the equipment you’re trying to protect. This is acceptable for most non-electronic equipment but may not adequately protect sensitive electronics.

The shunting protectors tend to be lower cost. For example, the LA110V lightning arrestor from Ananda Power Technologies retails for $49. The LA100V is a Silicon Oxide Varistor (SOV) especially manufactured for use in low voltage DC systems. The LA100V protects the system by clamping the voltage at 100 VDC and is rated to dissipate 50,000 Amps and 750 Joules of energy. This arrestor responds to surges very quickly and can clamp 10,000 Amps within 10 nanoseconds. The LA100V provides both differential protection (when there is 100 V between system positive and system negative) and common mode protection (when both system positive and system negative are 100 Volts above ground). This SOV type protector contains a harmless white powder, silicon oxide, which gradually melts as it absorbs surges. If the surge is above the rating of the LA100V, the case of the unit will rupture indicating the need for replacement.

In-Line Protection

The other basic protector design is called in-line (or series). These units actually process the power that travels through them under ordinary circumstances. You must respect their current limitations and you must specify ac or DC in addition to the turn-on voltage. In- line protectors impose a slight reduction in output voltage. These protectors do not tend to share the surge with your equipment, and may be indicated where electronics are involved.

PolyPhaser Corporation makes an in-line protector for solar module (or other DC) installations which drops 0.3 Volts at its 30 Amp maximum. 0.3 Volts represents

Below: The LA100V shunting type surge arrestor. Photo courtesy of Ananda Power Technologies, Inc.

72 Home Power #55 • October / November 1996

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