[TowerTalk] Bonding entrance panel to utility ground question
jim at audiosystemsgroup.com
Sun Mar 26 00:08:39 EST 2006
On Sat, 25 Mar 2006 18:46:56 -0800, Jim Lux wrote:
>Here is where it gets tricky. You'll have to look up the code sections to
>see if you can bond the antenna lightning protection ground to a electrical
>safety ground. I'm going to guess that it's not a good idea.
I will differ with you on that one, Jim. Under NEC, and most electrical
codes, ALL grounds within an installation are required to be bonded together,
including the lightning protection system. NEC (and most codes) state that
the lightning protection system ground cannot be the SOLE earth connection.
In general, ALL grounds and ground electrodes in a given installation should
be bonded together, and, as you have so elequently observed, making that
connection THROUGH the building is not the smartest idea. BUT -- as has also
been observed, lightning has HF spectra, and even the slightest inductance in
the bond can develop some very high potential differences and generate arcs.
I like the recommendation of getting that antenna to earth by the shortest
possible route (and without bends), then bonding it by the lowest inductance
means to all other earth connections and building grounds. But if the bonding
path is a long one around the perimeter, L can be quite high. This why W8JI
has correctly observed that the best place to bring antennas in is right next
to the power service (and power earth electrode). Unfortunately, that isn't
always practical when we're not building from scratch and can't make that
choice for the location of the ham shack.
Jim Brown K9YC
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