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[Towertalk] Ground loops

To: <>
Subject: [Towertalk] Ground loops
From: (Tom Rauch)
Date: Sat, 3 Aug 2002 11:02:31 -0400
> Each piece of equipment in the shack has a ground wire which goes
> directly to the coax entry point. Most equipment here is equipped with
> a 3 wire plug for power. Two of these wires go back to the service
> entrance ground rod. Have I not just created a ground loop? Or one big
> ground loop and several small ones?

Try this connection:

Pwr gnd--House gnd--equipment--shack gnd--ant twr gnd

That is a bad situation because any hits any place will pass through 
the house and equipment in the house. No ground is ever perfect.

Now if we have a common point that ties all of the external 
connections together (like at the service entrance ground) with the 
house connections leaving that one point to the shack, current will 
not flow through the house.

Everything entering the house should pass the service entrance and be 
grounded there, or you had better have a very low impedance 
connection between the service ground and everything entering the 
How does this arrangement work? Pretty well!

Last Sunday I had three direct hits on my 318ft tower within 15 
minutes. One of the hits was enough to blow a RG-8 cable completely 
out of a connector on the bulkhead feedthrough of the repeater shed 
next to the tower. All of our TV sets are now magnetized (they lost 
color purity, so I need to degauss them).   

The net damage, other than the TV screens being magnetized, was three 
protection diodes in the house on my control cables, one telephone in 
an outbuilding, and one skinny foil trace on the power sensing line 
of an external VHF amplifier connected to the cable that blew apart.

I have no lightning protectors anywhere, except a few RCS-8 switches, 
MOV's on power and telco lines, and some 1N4007 diode clamps on the 
24 control lines that run back 2500 feet. No modem damage, no 
appliance damage. No equipment damage (except the VHF amp that had a 
skinny hair-like trace that disappeared and the RG-8 cable feeding 
the bulkhead). All of my gear was connected, and I was in my workshop 
with test equipment running during the first hit (I got the hell out 
of there!).

It's all in the grounding.

We should always bring **everything** external to one point, and then 
into the building. At the radio room, we should have everything enter 
that room at one common point where it is all bonded. You'd be amazed 
at how much that means.

Of course I have other things, like perimeter grounds. But only 
because there are towers or antennas in every direction that connect 
to two separate buildings. I've got to remember to put MOV's on my 
well pump wiring some day soon though!

73, Tom W8JI 

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