What size ground wire for 30 amp subpanel

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Old 07-17-07, 09:26 AM
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What size ground wire for 30 amp subpanel

I pulled the wire, two hots, neutral, and ground, all #10's for a 30amp 220 V subpanel in a small granny flat. A) Should I run the ground, from the ground bar in the subpanel (yes the neutral is isolated) to the cold water system in addition to the ground bar? B)Does the ground wire to the ground bar need to be #10 or can I drop down to #12?

Thanks

Tom
 
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Old 07-17-07, 09:37 AM
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Is this sub panel in the same building as the panel supplying it?
 
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Old 07-17-07, 09:57 AM
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> to the cold water system in addition to the ground bar?

No.

> B)Does the ground wire to the ground bar need to be #10

Yes.
 
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Old 07-17-07, 10:01 AM
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Originally Posted by racraft View Post
Is this sub panel in the same building as the panel supplying it?
No, seperate building
 
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Old 07-17-07, 10:13 AM
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> to the cold water system in addition to the ground bar?

No.

Is this unsafe or just not necassary? It is the same cold water as the main house.
 
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Old 07-17-07, 10:17 AM
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> No, seperate building

Okay, you need an electrode. This can be either the underground cold water pipe or a copper-clad rod driven into the earth. If you opt to use the water pipe, you'll need to attach the #6 copper wire to the pipe within 5' of the point where the pipe enters the building.

To avoid some confusion regarding "ground wires": the equipment grounding conductor which is the ground between the main panel and the subpanel ground bus should be #10 copper. The grounding electrode conductor which runs between the subpanel ground bus and the grounding electrode (rod or pipe) should be #6 copper.
 
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Old 07-17-07, 11:03 AM
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OK, to make this clear is it #6 or #8 to the electrode?
to summarize
30amp 220v subpanel.
Seperate building from main house.
I'm suprised that I would need #6 for a 30 amp sub, but realize this would be the least path of resistance if that is the reasoning.
 
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Old 07-17-07, 11:09 AM
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It is a number 6, as stated. This size is not exactly based on the size of the sub panel, because it is not for a problem with the sub panel circuits.
 
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