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Old 02-04-2010, 03:45 AM   #16
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Quote:
Originally Posted by Scuba_Dave View Post
Actually with (3) #3' & a #6 as a ground you could use 1"....
You only need a #8 ground wire on a 100 Amp feeder, using #3 conductors. Only if you upsize your main conductors to a #2 are you required to upsize your ground wire to a #6.

We would use a #4 neutral conductor as well. I have yet to see any 100 Amp subpanel whose unbalanced load calculation exceeded the capacity of a #4 (85 Amps).

These numbers represent copper AWG wires with THHN/THWN or XHHW insulation.
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Old 02-04-2010, 09:05 AM   #17
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My uncle actually has a four inch long piece of 1-1/2" with threaded ends. I got it from him last night so I'll be using 1-1/2".
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Old 02-04-2010, 12:35 PM   #18
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I did not know that regarding the size of the neutral and ground wires for a subpanel. So I'm going to use (2) #3 for the hot connections, a #4 for the neutral, and a #8 for the ground connection. Is there a section in the NEC that talks about this and unbalanced loads?
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Old 02-04-2010, 12:37 PM   #19
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I did not know that regarding the size of the neutral and ground wires for a subpanel. So I'm going to use (2) #3 for the hot connections, a #4 for the neutral, and a #8 for the ground connection. Is there a section in the NEC that talks about this and unbalanced loads?
Check with your local Inspector 1st
Some do not seem to like an "undersized" neutral for whatever reason
Even tho by code it is allowed
I've always used the same size as the hots



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Old 02-04-2010, 12:45 PM   #20
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What about the ground wire? What is the reasoning for using a smaller ground wire?
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Old 02-04-2010, 01:55 PM   #21
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Ground wire does not carry power



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Old 02-04-2010, 02:09 PM   #22
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I know that; it only carries load excess load in the case of a short. But is it allowed to be of smaller diameter since it is assumed that a full load will not be passing through it. By that I mean, if there is a short in a 12/2 wire somewhere down the line, a #8 wire could carry that load?
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Old 02-04-2010, 03:08 PM   #23
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#8 wire is larger then 12/2 wire

A short to ground kicks the breaker off
An illegal bootstrap from neutral to ground may cause a ground to carry power



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Old 02-04-2010, 06:42 PM   #24
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Quote:
Originally Posted by faromic View Post
I did not know that regarding the size of the neutral and ground wires for a subpanel. So I'm going to use (2) #3 for the hot connections, a #4 for the neutral, and a #8 for the ground connection. Is there a section in the NEC that talks about this and unbalanced loads?
That is what we normally install, for a 100 Amp sub-feed.

The Code section you seek is 220.61:
Quote:
220.61 Feeder or Service Neutral Load
(A) Basic Calculation
. The feeder or service neutral load shall be the maximum unbalance of the load determined by this article. The maximum unbalanced load shall be the maximum calculated load between the neutral conductor and any one ungrounded conductor....
There are additional permitted reductions where the feeder includes loads such as electric ranges and dryers, and other prohibited reductions where the supply is fed from a 3 phase wye source.

As stated previously, I have yet to find a 100 Amp sub-panel whose maximum unbalanced load could exceed 85 Amps.
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Old 02-05-2010, 01:15 PM   #25
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Quote:
Originally Posted by Scuba_Dave View Post
Check with your local Inspector 1st
Some do not seem to like an "undersized" neutral for whatever reason
Even tho by code it is allowed
I've always used the same size as the hots
It's always best to use the same size Neutral as the other conductors. You might encounter a situation with an overloaded Neutral (if it's a smaller size.)
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