I think that this falls under "separately derived power" like a generator
would.
When using an isolation transformer on a boat the secondary center tap of
the transformer goes to the boats ground system which is separate from the
shore ground system. It is treated just like a generator as far as grounding
goes.
73
Gary K4FMX
> -----Original Message-----
> From: Carl [mailto:km1h@jeremy.mv.com]
> Sent: Wednesday, November 04, 2009 8:36 AM
> To: Gary Schafer; amps@contesting.com
> Subject: Re: [Amps] TL922 Power Plugs
>
> Im running 480V to the shop out back thru a pair of step up/step-down
> 10kva
> transformers. This uses a 3 wire run and has been in place for 20 years to
> run machine tools, compressor, welder, etc.
>
> Is it correct to have a ground rod at the shop end with the neutral
> grounded? If the building is metal should it also be grounded?
>
> This is getting confusing.
>
> Carl
> KM1H
>
>
>
> ----- Original Message -----
> From: "Gary Schafer" <garyschafer@comcast.net>
> To: "'Paul Christensen'" <w9ac@arrl.net>; <amps@contesting.com>
> Sent: Tuesday, November 03, 2009 10:10 PM
> Subject: Re: [Amps] TL922 Power Plugs
>
>
> >
> >
> >> -----Original Message-----
> >> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On
> >> Behalf Of Paul Christensen
> >> Sent: Tuesday, November 03, 2009 8:21 PM
> >> To: amps@contesting.com
> >> Subject: Re: [Amps] TL922 Power Plugs
> >>
> >> > My Neutral and Ground is connected at the main panel but also at
> >> > the barn 300 feet away. I am running a 3 wire 100 amp 240v power 4 00
> >> > aluminum line to the barn from a 100 amp 240v breaker located in my
> >> > main
> >> >distribution box. I didn't like the idea of a gnd neutral tie that
> far
> >> >away from
> >> > the barn, so I tied them together at the barn with a second ground
> rod
> >> > located
> >> >at the barn. Is that such a bad idea?
> >>
> >> See NEC 250.32(A) and (B). Since your 3-wire system is existing, the
> 4-
> >> wire
> >> requirement beginning with the 2008 NEC likely does not apply -- but
> may
> >> under your local code. New detached structure wiring generally
> requires
> >> 4-wire service whether or not there is a continuous metallic path
> between
> >> structures In no event should the neutral and ground come in contact
> >> again
> >> from the feeder path to the barn's sub-panel (as it seems to exists
> now).
> >> Being a detached building, the barn service entrance must be
> >> grounded/bonded
> >> to its own grounding electrode or grounding electrode system in
> >> accordance
> >> with Part III of NEC Section 250.
> >>
> >> Paul, W9AC
> >
> > Paul,
> >
> > If I am following what you are saying that is not correct. Under the old
> > rules with a 3 wire feeder to a detached building the neutral was to be
> > connected to the neutral and ground buss in the panel in the remote
> > building. A local ground rod was also to be installed and connected to
> the
> > neutral/ground buss at the detached building.
> >
> > The neutral and ground would also be connected together at the main
> panel.
> > They also stipulated that there were not to be any other metallic
> > connections between the two buildings such as water pipes, phone lines
> > etc.
> > that could possibly carry any neutral currents inadvertently.
> > Otherwise 4 wires would be required and the ground/neutral connection in
> > the
> > detached building had to be then kept separate as the new code states. A
> > local ground rod connected to the ground buss is still required at the
> > detached building.
> >
> > 73
> > Gary K4FMX
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
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