Afternoon Carl...
A very long time ago I asked the plant electrician where I worked at
the time about this very thing... now he told me that the the reason
you don't bond in two different areas on the same service had to do
with "fault current" between the neutral and ground... said current
could be very high during an "event" such as a lightning strike and
would normally go through that heavy link inside the panel but... if
that link was damaged on unconnected it would search out a similar
condition through out all the circuits connected to the panel and
upon finding one connected in the "wrong" way would dump power
through the connected equipment and the low voltage, low current line
cord instead of the heavy link most likely causing a fire...
Was this electrician right? I don't know but he didn't want bonding
anywhere except the panel...
73, Ott
At 09:36 AM 11/4/2009, you wrote:
>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
> >
> > _______________________________________________
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> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
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