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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