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Re: Lightning and neutral grounding



If the Neutral line goes to ground at the Service entrance and the house 
ground wires do also then they are common at the service entrance.  The 
ground wire then comes back through the house wiring to the ground terminal 
on the 3 conductor power lead cord to the radio.  The ground lead goes to 
the chassis inside the radio as a safety ground.  The RF ground terminal on 
the radio as well as the coax shield (via the antenna) both go to the 
outside ground rod by the station.  A number 4 wire runs from that ground 
rod to the TV antenna ground rod and on around to the service entrance 
ground rod.  It seems to me that the service entrance grounded neutral and 
the safety ground in the house wiring are tied together and fan out from 
the service entrance.  However there is another path from the house ground 
wire back to the service entrance, going via the radio chassis to the RF 
ground rod and back via the three strapped ground rods to the service 
entrance neutral.  This has always bothered me, especially now that I hear 
thunder in the west :-)  I disconnect all coax leads at my coax patch 
panel, open the power at the desk fused box, unplug all rotor cables, the 
KCT to PC cable and power down all PCs when I hear thunder approaching.  I 
have a whole house surge surpressor in the service entrance box on the 
house side of the circuit breakers.  I respect that stuff.

Jon Ogden wrote:
> 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?
> 
> 
> Roy,
> 
> 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.
> 
> 73,
> 
> Jon
> NA9D
> -------------------------------------
> 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."
> 
> 


-- 
73, Roy -- W0SL

E-Mail: rdwelch@swbell.net
Home Page: http://home.swbell.net/rdwelch

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