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sub panel detached building #97406
02/18/06 08:37 PM
02/18/06 08:37 PM
watersparkfalls  Offline OP
Member
Joined: Mar 2005
Posts: 222
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

2017 / 2014 NEC & Related Books and Study Guides
Re: sub panel detached building #97407
02/18/06 08:39 PM
02/18/06 08:39 PM
watersparkfalls  Offline OP
Member
Joined: Mar 2005
Posts: 222
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.

Re: sub panel detached building #97408
02/18/06 09:13 PM
02/18/06 09:13 PM
G
George Little  Offline
Member
Joined: Jan 2004
Posts: 1,489
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?


George Little
Re: sub panel detached building #97409
02/18/06 10:02 PM
02/18/06 10:02 PM
S
ShockMe77  Offline
Member
Joined: Jun 2005
Posts: 821
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: https://www.electrical-contractor.net/ubb/Forum1/HTML/006874.html

Re: sub panel detached building #97410
02/18/06 10:03 PM
02/18/06 10:03 PM
S
ShockMe77  Offline
Member
Joined: Jun 2005
Posts: 821
Rahway, New Jersey

Re: sub panel detached building #97411
02/18/06 10:12 PM
02/18/06 10:12 PM
E
earlydean  Offline
Member
Joined: Dec 2003
Posts: 751
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


Earl
Re: sub panel detached building #97412
02/18/06 10:16 PM
02/18/06 10:16 PM
E
earlydean  Offline
Member
Joined: Dec 2003
Posts: 751
Griswold, CT, USA
The neutral may only be derated if there is sufficient straight 240 volt loads to warrant it.
see 220.22


Earl
Re: sub panel detached building #97413
02/18/06 11:52 PM
02/18/06 11:52 PM
M
markp  Offline
Member
Joined: Apr 2004
Posts: 60
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.


Mark
Kent, WA
Re: sub panel detached building #97414
02/19/06 02:34 AM
02/19/06 02:34 AM
S
ShockMe77  Offline
Member
Joined: Jun 2005
Posts: 821
Rahway, New Jersey
My bad.

Yes, a grounding electrode MUST be installed on any detached building.

Re: sub panel detached building #97415
02/19/06 11:09 AM
02/19/06 11:09 AM
S
Speedy Petey  Offline
Member
Joined: Aug 2003
Posts: 173
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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