Lightning Protection using Relays

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The topic of lightning protection of our radio equipment and everything else in our homes wisely comes up often in the various ham related email lists on the Internet.

A particular thread on one of these lists spoke of ways to disconnect coax, rotator control lines, etc. at or near where they come into the building. One implementation described by some fellow used relays to disconnect things so he could through one switch and instantly isolate his radios from the antennas.

The problem with this is obvious as the gap between the open contacts of a relay are easily breached by the enormous energies associated with lightning events.

The reason why can be understood with the following value of the breakdown potential of a air gap…

3 million volts per meter

Translate this to, say, a 1 mm gap between the open relay contacts results in only 3,000 volts before breakdown begins.

3,000 volts sounds like a lot, but to a lightning surge it really amounts to nothing. Remember lightning travels far more than that small gap to get to ground and won’t have any problem making the final jump.

So, really, the best approach to disconnecting your equipment remains detaching coaxial cables and ensuring they are far away from the connectors.

Of course designing in good lightning protection devices on a good single point ground (SPG) is still urgently suggested.

You spent good money on your Icom, Kenwood, Yaesu, Ten-Tec, Elecraft radio… probably a lot. No ham shack is complete without spending, say, another 10% of the radio cost on lightning protection from PolyPhaser, Alpha, etc.

Consider good lightning protection cheap insurance for your radio investment. Don’t be cheap.

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