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#97406 - 02/18/06 04:37 PM sub panel detached building
watersparkfalls Offline
Member
Registered: 03/08/05
Posts: 212
Loc: Washington...Not DC
i have a sub 50 amp sub panel that i want to put in a detached maint/gar building.
to save money on wire i am going to run two #6's for the lines and one #8 for the neutral(derating the neut)along with a #10 ground. my question is does this sound code compliant, we derate neutrals for the service feeders and this is going to be a feeder so it seems very complicit to me.

am i on the right page? any codes that i am missing which would forbid this derating?
thanks guys,
h20
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#97407 - 02/18/06 04:39 PM Re: sub panel detached building
watersparkfalls Offline
Member
Registered: 03/08/05
Posts: 212
Loc: Washington...Not DC
oh yea it is a metal building which i will bond the beam structure and will drive two ground rods down at the building too.
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#97408 - 02/18/06 05:13 PM Re: sub panel detached building
George Little Offline
Member
Registered: 01/18/04
Posts: 1488
Loc: Michigan USA
By not knowing what your load is, I can't tell you that you can or can't derate the neutral. Also, I would be interested in how you terminate the neutral and ground wires in the sub panel. Where do you connect the Grounding Electrode Conductor in the sub panel?
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George Little
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#97409 - 02/18/06 06:02 PM Re: sub panel detached building
ShockMe77 Offline
Member
Registered: 06/11/05
Posts: 821
Loc: Rahway, New Jersey
There's no need to install ground rods if you run a separate equipment grounding (bonding) conductor (E.G.C.) to the detached garage.

See more about this topic here: http://electrical-contractor.net/ubb/Forum1/HTML/006874.html
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#97410 - 02/18/06 06:03 PM Re: sub panel detached building
ShockMe77 Offline
Member
Registered: 06/11/05
Posts: 821
Loc: Rahway, New Jersey
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#97411 - 02/18/06 06:12 PM Re: sub panel detached building
earlydean Offline
Member
Registered: 12/22/03
Posts: 751
Loc: Griswold, CT, USA
Hold on. You must ALWAYS install a grounding electrode system for a detached building with more than a single multiwire branch circuit. It doesn't matter if your have three or four wires; with or without an equipment grounding conductor.
see 250.32
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Earl
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#97412 - 02/18/06 06:16 PM Re: sub panel detached building
earlydean Offline
Member
Registered: 12/22/03
Posts: 751
Loc: Griswold, CT, USA
The neutral may only be derated if there is sufficient straight 240 volt loads to warrant it.
see 220.22
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Earl
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#97413 - 02/18/06 07:52 PM Re: sub panel detached building
markp Offline
Member
Registered: 04/12/04
Posts: 60
Loc: Kent, WA, USA
If your neutral busses are specifically listed at 75C and you use 75C rated wire, then #8 copper is fine for a 50A feeder because that wire is still rated at 50 amps.
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Mark
Kent, WA
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#97414 - 02/18/06 10:34 PM Re: sub panel detached building
ShockMe77 Offline
Member
Registered: 06/11/05
Posts: 821
Loc: Rahway, New Jersey
My bad.

Yes, a grounding electrode MUST be installed on any detached building.
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#97415 - 02/19/06 07:09 AM Re: sub panel detached building
Speedy Petey Offline
Member
Registered: 08/29/03
Posts: 173
Loc: Upstate, NY
Quote:
Yes, a grounding electrode MUST be installed on any detached building.

...that is fed with a feeder.
If you only run a circuit no rod is needed.
See: 250.32
_________________________
Speedy Petey

"Anyone who has never made a mistake has never tried anything new." -Albert Einstein
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