That sounds about normal. The relatively small wire bonding the secondary
neutral, pig shell, and probably all the other hardware to the line return
wire and then down to a ground rod has a couple purposes, none related to
actually delivering you power... First that wire keeps all the hardware at
the same potential. This prevents stray voltage pickup on the hardware from
damaging the pole, and any lineman that may be working on it! Second it
provides a return path to blow the primary breaker/fuse if there is a fault
in the transformer or a dropped wire or anything else that would put the
primary voltage on the service drop or other hardware. Also by bonding
everything together (including guy wires if used) they prevent stray voltage
between someone standing on the ground and any exposed ground level
hardware... the so called 'step' and 'touch' potentials. And finally
bonding all the hardware also prevents rfi from stray voltages causing
corona or arcing on the pole.
One important thing... The ground rod at the pole can not be assumed to
provide an adequate return path to replace the neutral in the triplex wire
to the house entrance. The resistance through the ground, even with a large
ground system at the house, just isn't low enough to be a decent return
path. As anyone who has had that neutral fail knows, all sorts of bad
things happen if that happens... including equipment damage and even fires,
and the circuit breakers in the house will not protect you from it!
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Tom Rauch
> Sent: Saturday, October 08, 2005 13:12
> To: Ian White GM3SEK; towertalk@contesting.com
> Subject: [TowerTalk] Pole Pig Transformer wiring
>
> > Jim Lux wrote:
> > >> The power company also grounds the
> > >>neutral connection at the transformer to earth ground.
> > >
> > >Not necessarily.. for the same reason as you have a
> single interconnect
> > >between neutral and ground. You don't want neutral
> return currents
> > >flowing back to the transformer via the ground path.
>
> Ian Replied:
> > Interesting... the power companies in the UK take a
> different view. In
> > the event of a neutral break in their local distribution
> system (230V
> > single-phase, neutral close to earth potential) they'd
> rather have the
> > return current flowing back through earth than create a
> shock hazard due
> > to the neutral becoming hot.
> >
> > Therefore they almost always earth the neutral at the
> transformer,
> > and/or anyplace else they conveniently can.
>
> I had a look at the transformer here.
>
> I have two drops. One to a distribution pole with a meter
> and a pair of dual 200 amp mains that feeds my radio room
> and all the outbuildings, the other drop feeds a single 200A
> dual mains for the normal house wiring.
>
> At the transformer the heavy neutrals bond directly with
> very heavy wire to the bare distribution ground wire passing
> the pole. The center tap of the pole pig has what looks like
> a number 6 solid copper wire to the metal can and to the
> ground wire running down the pole. That ground wire bonds to
> the neutral wire running down the street.
>
> The ground path at the pole is from the 240V winding CT to
> earth and to the HV neutral at the road through a small
> gauge wire, perhaps number 6 AWG. The heavy bonding is from
> the bare triplex drop wire directly to the street neutral,
> which is the return for the 7,200 volt distribution line.
>
> Very clearly the utility wants the major bond to be with the
> 7200 volt return, a much smaller conductor goes from the pig
> CT to the pole ground wire...which eventually after a few
> splices connects to the area distribution neutral.
>
> What do others see outside their houses in the USA?
>
> 73 Tom
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
> any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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