At 09:08 PM 3/25/2006, Jim Brown wrote:
>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.
I'll agree with that. All grounds (in the same building) MUST be bonded
together. My comment (which, now that I read it, was poorly worded) was
whether it's "legal" to bring that lightning ground (from the polyphasers)
*into the middle* of the "grounding conductor" (greenwire ground) from the
well pump. (A "T" intersection, if you will.)
I think you'd be better off running a separate bonding conductor from the
"lightning ground rods" to the "utility entrance ground", rather than
sharing part of the run of the well pump grounding conductor. What I don't
know, off hand, is whether the code would even allow such a sharing of the
conductor.
>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.
And there's the tradeoff..
Of course, he has a bunch of ground rods right at the polyphasers, so one
thought might be that you want a fairly inductive, but code legal,
connection between the lightning ground rods and the utility ground
rods. That way, in normal operation, you don't have an issue with grounds
at different voltages, etc., but when the lightning hits, the transient
isn't coupled (as well) into the building's green wire grounding system.
(Or, into that nice pump immersed in water a hundred feet down the well)
>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 what if the ground at the antenna entrance is "better" (lower
impedance, etc.) than the "code ground" at the utility entrance. This is a
scenario that I think is actually quite common. The code ground is
designed for 60Hz, not RF, and the inductance is not usually
considered. On the other hand, hams obssess about getting a good RF ground
(all those "how do I most effectively string this 100 pounds of copper wire
I got at the hamfest" articles and posts and websites), which, to a first
order, probably is a better lightning dissipation ground than the utility
ground.
> 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
Jim, W6RMK
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