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Old 06-03-2011, 02:01 PM   #1
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Ground conductor size for feeder


So the inspector, as mentioned in the other thread, is requiring a continuous ground from the main panel to the detatched garage subpanel. I have a conduit run that is continuous rigid metal conduit between 2 junction boxes, the conduit is grounded on both ends, the junction boxes are grounded on both ends, but there is PVC between each junction box and its respective service panel.

He would accept EMT betwen the junction boxes and the service panel, or he would accept a conductor running with the feeder. My calcs say the conductor is the cheaper way to go.

Am I correctly reading and applying Table 250.122 by interpretting that for 100 amp subpanel I need an 8 gage copper conductor?

Does it matter if its solid or stranded?

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Old 06-03-2011, 02:22 PM   #2
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Ground conductor size for feeder


Yes, you need 8g wire. I don't think solid or stranded matters. I'd run stranded, way easier to deal with.

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Old 06-04-2011, 07:39 AM   #3
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Ground conductor size for feeder


Correct, #8 Cu EGC for a 100A sub. #8 and larger installed in conduit has to be stranded. It would also have to be green or bare.
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Old 06-04-2011, 08:47 AM   #4
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Ground conductor size for feeder


Arg... I bought #8 solid last night, cut wire of course so I can't return it. Are you certain of that? 250.118 says solid or stranded and doesn't seem to say anything about #8 or larger.

Also, by problem is I have a rigid conduit I'm using between junction boxes with PVC between the junction boxes and the panels, but I have #6 to a ground clamp on one side and #4 to a ground clamp on the other... 250.118 reads as "
The equipment grounding conductor run with or enclosing
the circuit conductors shall be one or more or a combination
of the following"

Which I read as saying I can use the rigid in combination with the wires. Is my interpretation that far off that I can't point the inspector at the code and tell him he's wrong?
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Old 06-04-2011, 09:12 AM   #5
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Ground conductor size for feeder


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Arg... I bought #8 solid last night, cut wire of course so I can't return it. Are you certain of that? 250.118 says solid or stranded and doesn't seem to say anything about #8 or larger.
310.3 (which I don't see being superceded/excepted in Art 250)

250.118 does mention that it can be solid, but doesn't state how it can be used. 250.120 (EGC Installation) mentions that it be installed in accordance with applicable provisions in the code.

If I missed something, I'm all ears....
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Old 06-04-2011, 09:22 AM   #6
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Ground conductor size for feeder


Quote:
Originally Posted by WillK View Post
Also, by problem is I have a rigid conduit I'm using between junction boxes with PVC between the junction boxes and the panels, but I have #6 to a ground clamp on one side and #4 to a ground clamp on the other... 250.118 reads as "
The equipment grounding conductor run with or enclosing
the circuit conductors shall be one or more or a combination
of the following"

Which I read as saying I can use the rigid in combination with the wires. Is my interpretation that far off that I can't point the inspector at the code and tell him he's wrong?
From what it sounds like, all you did was bond the rigid pipe. The fact that the j-boxes have plastic between them and the panels is why the rigid is not your EGC, especially if a EGC wasn't run from the panels.
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Old 06-04-2011, 10:35 AM   #7
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Ground conductor size for feeder


FYI. 4 wire feeders have been required since the 2008 code cycle. How could you pull 3 wires when you needed 4? Now you need to get another wire into the conduit. Since you are not a professional, you might have to pull all of them out to get one in.
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Old 06-04-2011, 04:12 PM   #8
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Ground conductor size for feeder


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FYI. 4 wire feeders have been required since the 2008 code cycle. How could you pull 3 wires when you needed 4? Now you need to get another wire into the conduit. Since you are not a professional, you might have to pull all of them out to get one in.
Well the inspector is aware that as of April we're on the 2008 code cycle, but he has been clear that IF I replaced the section that I have PVC with EMT that I would not need the 4th ground conductor. BUT since a 50' conductor at 8 ga. copper costs less than 2 EMT runs at 3' each with all associated fittings, plus is simpler, that is what I am doing hence the question in the OP. The question about the particulars of whether code allows a combination of wires and conduit is academic..

At any rate, I don't see where pulling all the cables out is necessary. My conduit is generously oversized, I have 3 conductors of 1/0 aluminum feeding the panel and they're inside 2" rigid metal. I pulled 14 ga. conductors for my 3-way switch without even having my wife assist. There's plenty of capacity for an easy 8 ga. wire pull.

What I have been working off of is Michigan electric code from when it was based off 2005 NEC, Michigan has not yet (that I know of) made the update to 2008 NEC available for download online.
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Old 06-04-2011, 04:24 PM   #9
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Ground conductor size for feeder


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310.3 (which I don't see being superceded/excepted in Art 250)

250.118 does mention that it can be solid, but doesn't state how it can be used. 250.120 (EGC Installation) mentions that it be installed in accordance with applicable provisions in the code.

If I missed something, I'm all ears....
Well, the way I read it, the exception in 310.3 reads:

Exception: As permitted or required elsewhere in this Code.

And 250.118 is titled "Types of Equipment Grounding Conductors" I'm not sure how much more clear it can be that the use is as an equipment grounding conductor... Unless the term is different for a ground wire running with a subpanel feeder?

I appreciate the advice, and if I hadn't already bought the solid I would be buying stranded. Being that I've bought it, and it's not crystal clear that the exception is not in place, I plan to feed the solid wire and see if the inspector passes it. If he doesn't I'll just have to use the solid to pull through a stranded wire and spend another $34 that I can't really spare.
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Old 06-05-2011, 10:59 AM   #10
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Ground conductor size for feeder


250.118 (1) does permit the use of a solid conductor as an EGC and would be the correct term “for a ground wire running with a subpanel feeder”, but it does not exempt 310.3, nor does 250.120.
310.3 does have that exception, however I do not find anywhere in the code, including 250.118, stating that 310.3 is exempted. Since 310.3 does not specify any particular article or section that it applies to, any article or section that would allow the 310.3 exception would be stated in that article/section. If it isn’t stated an exception is permitted, it isn’t.

I’m sorry that this is your situation at the moment. Like you said, maybe he won’t catch it. I’m not advocating it, just trying to point out the requirements in the code.
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Old 06-05-2011, 03:30 PM   #11
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Ground conductor size for feeder


I agree with SD515
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Old 06-05-2011, 05:58 PM   #12
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Ground conductor size for feeder


Okay, so that aside, can anyone explain the rationale for requiring stranded and not allowing solid for 8 AWG and larger?
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Old 06-05-2011, 06:06 PM   #13
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Ground conductor size for feeder


I think it is just to make it easier to install in a conduit and to prevent damage to other conductors.
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Old 06-05-2011, 06:53 PM   #14
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Ground conductor size for feeder


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.... I have 3 conductors of 1/0 aluminum feeding the panel and they're inside 2" rigid metal.....
Since you have "oversized" your feeder conductors (#1 AL would have been sufficient for 100 Amp), the inspector-critter may require you to upsize your EGC as well. If he is as anal as you say he is, I'd be willing to bet you will have to use at least a #6 copper ground wire to satisfy him. See section 250.122(B) of the NEC.

Who wants to place bets with me on this one>? Any takers?
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Old 06-05-2011, 07:09 PM   #15
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Ground conductor size for feeder


If he doesn't accept 8 AWG solid that would probably work out fine since HD doesn't have 8 AWG stranded and I'd have to go to 6 AWG to get stranded anyway.. All the more reason to hold off on the purchase until he gives his word. (another reason being that HD closed 9 minutes ago)

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