Sent: Sunday, July 27, 1997 10:54 AM
Subject: Annual maintenance
Bob; thanks for your reply on Towertalk on 7-27 about ground rods, etc. You
generated one question which may have been discussed before (or maybe not)
about annual maintenance. I would assume that means checking and cleaning
connections, replacing corroded parts, etc. Would it also mean digging up
ground rods to check condition? Without a megger is there any other way? I
guess the multiple stake and voltage/current measuring method that I have
seen in your (Polyphaser) pubs would do it.
>The multiple stake IS the Megger (or equivalent). I am unaware of any
other means to check the value of the ground system. Remember that
the ERT (Earth Resistance Tester) measures at 100 Hz and not at the
frequencies where lightning energy is at a relative peak (other than at dc)
which occurs between 10 and 1000 kHz. There is energy into the low GHz
range, which is why skin effect is an issue. There is no correlation between
the 100 Hz reading and how good the system will be at 10 kHz. The rule of
thumb is to try to achieve 10 Ohms or less, 5 or less being the true goal. As
I've mentioned, one can have a 3 Ohm measurement and still incur damage
from lightning because the ground material used (e.g. #6) was just too
inductive at lightning frequencies to be "seen" as a good ground by the surge.
In summary, is a checklist published anywhere? If so and it is of general
interest, would you stick it on the reflector?
>We have a checklist, but I have no way of posting it. It is part of our book
"The 'Grounds' for Lightning and EMP Protection" as one of the appendices.
It is more for establishing a ground system at a commercial site. The book
runs $22.95 ppd. and we give 10% off to hams (make sure you let us know
the callsign). Free (until they run out, and I don't know if I was successful in
convincing the powers-that-be to obtain more copies) is some grounding info
written specifically for hams by hams. It's called the Hamfest Bulletin. If
out, ask the person who is assisting you to mail you our newsletter (Striking
for Feb and May 1994 as the Hamfest Bulletin originally appeared as a two-part
article in the newsletter.
73, Bob AA0CY
Many thanks. I appreciate the things you have to say on the Towertalk; it's
good to have you as a resource. 73, Jim Long, K4UHL
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