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Posted By: SCS sub panel in seperate structure - 11/12/03 02:22 AM
im installing a 100 amp sub in poll barn ,im using PVC and pulling wires .. do i need to pull a ground wire with my feeder conductors ,there will be 2 wires and a nuetral in pipe ,i know i have to drive an additional ground rod at the other building
Posted By: Ryan_J Re: sub panel in seperate structure - 11/12/03 02:31 AM
250.32 allows you to use the grounded conductor of the feeder circuit to attach to the grounding electrode of the seperate structure, if you do not pull an equipment grounding conductor.
Posted By: Roger Re: sub panel in seperate structure - 11/12/03 02:32 AM
Will there be any other conductive paths to the barn? (ie phone line or metalic water pipe etc...)

If so yes, and you would isolate the neutral from the EGC and the ground rod (GEC)connections.

Even if you are not going to have any other conductive paths right now, it is still the best way to do this. (plan for the future)

Roger
Posted By: Roger Re: sub panel in seperate structure - 11/12/03 02:36 AM
I should have also pointed to 250.32 as Ryan did.

Specificaly 250.32(B)

Roger
Posted By: SCS Re: sub panel in seperate structure - 11/12/03 02:39 AM
so i should add the EGC
im running 1/0 copper what size should the EGC be ??
Posted By: SCS Re: sub panel in seperate structure - 11/12/03 02:41 AM
did i say thank you for the fast reply ??
Posted By: Ryan_J Re: sub panel in seperate structure - 11/12/03 02:45 AM
Your welcome.

If you decide to use an equipment ground, you cannot use the nuetral for attachment to the grounding electrode.

If you do not pull an equipment ground you may use the nuetral for attachment to the grounding elctrode.

Dealer's choice!
Posted By: Ryan_J Re: sub panel in seperate structure - 11/12/03 02:48 AM
I'm sorry i missed half of your question. REmember that EGC's are driven by the size of the breaker, not the size of the conductor. 250.122 tells me that #8 is fine.
Posted By: SCS Re: sub panel in seperate structure - 11/12/03 02:51 AM
thanks guys
Posted By: Roger Re: sub panel in seperate structure - 11/12/03 03:03 AM
SCS, Welcome to the forum.

I personaly would install the EGC.

Roger
Posted By: Ryan_J Re: sub panel in seperate structure - 11/12/03 03:05 AM
I would too. EGC's are good things. As Roger said, welcome. And do come back often, there is a lot of knowledge here (like Roger)!
Posted By: SCS Re: sub panel in seperate structure - 11/12/03 03:10 AM
that is my thought also,thanx
Posted By: iwire Re: sub panel in seperate structure - 11/12/03 08:22 AM
In this case the size of the conductors will determine the size of the EGC.

Quote
250.122(B) Increased in Size. Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to circular mil area of the ungrounded conductors.

It is a 100 amp panel but you are running 1/0 awg I imagine for voltage drop reasons.

If we figure the normal size for a 100 amp feeder is 3 awg with a circular mil area of 52,620, and now you increase to 1/0 awg with a circular mil area of 105,600 the ratio between these two conductors is essentially 2.

Table 250.122 shows a 8 awg ground for a 100 amp breaker.

8 awg has a circular mil area of 16,510.

16,510 x 2 = 33,020 circular mils.

The smallest conductor that is more than 33,020 circular mils is a 4 awg with a circular mil area of 41,740.

So even though Table 250.122 shows an 8 awg ground for a 100 amp over current device we have to follow 250.122(B) and increase the size in proportion to the ungrounded conductors.

In this case that means a 4 awg ground with the 1/0 copper ungrounded conductors.

For extra fun, [Linked Image]

What size grounding conductor would be needed on a 30 amp circuit using 4 awg as the ungrounded conductors?

Think of this as a long circuit for site lights around a building.

Bob

Edit: I agree with Roger and Ryan, I also would pull an EGC. [Linked Image]




[This message has been edited by iwire (edited 11-12-2003).]
Iwire, my guess is 6.

Where do you get the circular mils chart?
Posted By: Roger Re: sub panel in seperate structure - 11/12/03 05:19 PM
Spark Master Flash, table 8 in chapter 9.

Roger
Thanks, Rog!
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