Jim,
I'm surprised your grounds are equal "to the microvolt". To me, that
indicates that no current is flowing in either, not even reactive, or
else they really are bonded together in some way. A practical ground
is going to have a resistance of a few ohms, in my experience. And no
two independent grounds will have the same resistance. So a current
of even a microamp will produce microvolts of differential.
That's neither here nor there. The thing to be concerned with is what
happens under fault conditions. What if there's a short in the wiring
that delivers 100 amps into the protective AC ground? (Let alone a
lightning event.) Under those conditions, you want to be sure that
your ham gear is not in the loop. If your 3rd wire AC ground goes to
your rig, and your local radio ground is separate, you'll get a good
fraction of the fault current going through the radio. Bad!
I solve this by running all my station AC through a Polyphaser PLDO
protector, which is bolted to my single point ground plane. That's
where the 3rd wire AC meets my ham ground system. I observed a
fraction of a volt of AC between the grounds before connecting them.
Now, any current surge will go from the 3rd wire to the SPG and my
equipment should not see it. See
http://blog.aa6e.net/2005/03/in-shack-ground-system.html .
(The PLDO is there mainly to absorb voltage surges on the hot and
neutral wires, not for grounding, but it does add discipline to the
grounding situation.)
73 Martin AA6E
On 11/29/05, JAMES BRASSELL <jimbrass@bellsouth.net> wrote:
> Hey, All.
>
> Just a quick observation and question. I have read many posts on this site
> about having the station and AC mains grounds tied together. For my
> observation, when you have a separate station ground (and I do; a good one)
> and all pieces of equipment are tied to that ground and the ground wire from
> the AC plug is tied to the equipment chassis then you have effectively tied
> the AC mains ground to the station ground. I have measured from the AC mains
> ground to the station ground and it is zero ohms, with no voltage (to the
> microvolt between them). I have looked in the equipment and the AC ground is
> tied directly to the chassis, not through a board. My question is, if the
> equipment is grounded and you have a good AC mains ground is that not tying
> the mains and station grounds together? I could see where one might have a
> problem if the ground in the equipment was achieved through a circuit board
> and the equipment was not otherwise grounded. I feed two verticals, GAP
> Titan an
d
> Voyager, and run 1500 watts into them on a regular basis without any RF
> problems. What say you?
>
> Jim, K4ZMV
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--
martin.ewing@gmail.com
http://blog.aa6e.net
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