If you have ever seen the result of a lightning
strike on electronic equipment, then you know how devastating it can be - often
total destruction that includes molten metal. Woe be unto any human operator who
happens to be in contact with it at the time of the strike. Unprotected antennas
are begging for contact. Shortly after leaving a company where I worked on a Tx/Rx
system for a phased array weather radar I got word that the indoor equipment rack
took a major hit because the guy who maintained the site forgot to reconnect a lightning
rod system cable after moving it during snow removal. I was glad not to be there
to have to repair everything.
A lot of knowledge has been gained both
in lightning properties and strike mitigation practices. A big part of properly
instituting a lightning protection system is assessing strike risk and then designing
and implementing the necessary lightning rods (aka air terminals), cables and connectors,
surge protectors, and grounding rods. The
Relay League (ARRL) provides a lot of resources for accomplishing this objective,
including publishing articles like "Lightning
Protection for the Amateur Radio Operator's Home," in the June 2017 issue of
QST magazine. In fact, the ARRL considers the dissemination of this data
so important that it makes it available even to non-subscribers.
One resource provided is a page on the East
Coast Lightning Equipment website with a
NFPA 780 Simplified Lightning
Risk Calculator for calculating whether your site should have lightning protection
installed. Enter the dimensions, material composition, property type, and lightning
strike frequency (map
provided), then it generates a 2-page PDF file with the results. The screen shots
given here are for RF Cafe headquarters in Erie, Pennsylvania, both with and without
a 3' antenna mast. You can see how the strike risk area doubles with the presence
of the mast.
In the Northeast region where
I live, the estimated cost of lightning protection per square foot of floor area
is about 95¢ for copper parts. My house is 912 ft2 and garage
is 330 ft2 for a total of 1,242 ft2. That results
in a cost of about $1,180 - not too awful. I installed a 2-pole, whole-house lightning
arrestor at my circuit breaker panel many years ago, and just this year I installed
a separate lightning arrestor + brownout protector on my air conditioner compressor.
However, I still do not have a lightning rod. One advantage my house has is that
the power lines in the neighborhood are on poles and on my side of the street, so
I benefit somewhat from the lightning cable that runs on top of all the other wires.
That, and the tallest trees in the immediate area are in the neighbors' yards.
Until I do get around to putting in lightning rods, I'll be sure to do as my
parents taught me to do during a severe lightning storm: unplug valuable equipment,
don't touch the phone or water pipes, and stay away from windows.
Posted May 31, 2017