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Re: Lightning and neutral grounding

on 3/11/03 11:50 AM, Roy Welch at rdwelch@swbell.net wrote:

> If the shack equipment has three conductor AC power leads, the ground lead
> is usually connected to the equipment chassis.  This ground is carried via
> the metal chassis to the braid conductor of any coax cable coming from the
> antennas to the shack equipment.  If the antennas are connected to an
> external ground rod, haven't you already connected the neutral conductor to
> ground at a point other than the entrance ground?  I see no way of avoiding
> this if the house ground wires are tied to the equipment chassis.  If this
> is the case, why not connect the ground wire on the radio desk phases to
> the 240v neutral conductor at the desk instead of taking a separate ground
> lead all the way back the the entrance panel?


Your radio equipment should be grounded, you are correct.  But running that
ground via the electrical system as you propose is not very helpful.  It
helps from a safety point of view, but from an RF point of view, it isn't
useful.  The equipment chassis ground should be grounded to earth by as
short a run of ground line as possible.  Going to the electric box inside
the house doesn't help in terms of RF.  Too much inductance.

I see your question, but let me ask one of you:

If the neutral in AC wiring is eventually connected to ground at the service
entrance, why have a third line that is grounded anyhow.  Why not just
ground through neutral?

Well, there's many reasons for that.  First of all, if something happens to
that neutral wire, you suddenly lose all ground.  Also, many times you will
see the hot and neutral lines across an AC transformer.  That AC transformer
is not usually grounded on the neutral side (if ever) while the chassis can
be grounded.  So you can have some differences in potential there.  If
there's a fault somewhere else in the house and the ground line is tied to
your neutral, then you could have problems.

But specifically to your question and I've read it multiple times, I think
it goes back to the fact that in your equipment, the AC is almost always fed
to a transformer.  The transformer then effectively isolates the neutral
from everything else and so the neutral is not connected in any way to the
chassis.  You can check this by removing the plug on the back of the radio
and measuring the resistance between the neutral line and the chassis.  I
think you will find an open circuit.


Jon Ogden
NA9D (ex: KE9NA)

Citizen of the People's Democratic Republik of Illinois

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

http://www.qsl.net/na9d   <- Updated on 1/22/03!!!

"A life lived in fear is a life half lived."

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