Proper way to ground a subpanel

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Old 02-04-11, 06:39 PM
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Proper way to ground a subpanel?

I'm working towards putting in a 60A sub-panel with a generator breaker lockout device (SquareD that has a 60A main panel breaker and a 30A generator breaker).

It will be fed using a 60A single pole breaker using #6, with the neutral going from an empty hole in the main panel's neutral bar to the (isolated) neutral bar in the sub-panel.

I'll be using a 1-1/2" offset nipple to mechanically join the panel (200A CH) to the sub-panel, which bonds them. Do I run a separate #10 green ground wire from the sub-panel's equipment ground bar and connect it to the same ground clamp to which the main panel's ground is connected? Run #10 bare ground from the subpanel's equipment ground to the main panel's ground bar? #8?

Thanks for the assistance.
 

Last edited by chieftaing; 02-04-11 at 07:31 PM. Reason: Updated some wire gauges.
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Old 02-04-11, 08:10 PM
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I'll be using a 1-1/2" offset nipple to mechanically join the panel (200A CH) to the sub-panel, which bonds them.
Assuming you are using the factory punched concentric knockouts for the 1 1/2" offset nipple (the largest being for 2 1/2" conduit), you should use a 1 1/2" bonding bushing on each end of the offset nipple to effectively ground it and the subpanel your are attempting to bond to it. I would use a #10 green insulated grounding conductor terminated at both ends like you suggested, but I would also route it through the ground clamp on each bonding bushing. A 1" offset nipple would be plenty large for this.
 
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Old 02-07-11, 07:35 PM
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Alternative: Run the #10 ground wire as you described.

"The knee bone is connected to the thigh bone is connected ..."

The subpanel frame (aka "can") is bonded to the ground bus bar furnished with it which is bonded to the #10 wire you ran through the nipple which wire is bonded to (you screwed it to) the ground bus bar in the main panel which is bonded to the main panel frame. Ergo the subpanel is now grounded to the main panel. According to NEC 250.122, circuits breakered at 30 to 60 amps use a #10 ground wire.
 
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Old 02-07-11, 08:09 PM
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Originally Posted by AllanJ View Post
Alternative: Run the #10 ground wire as you described.

"The knee bone is connected to the thigh bone is connected ..."

The subpanel frame (aka "can") is bonded to the ground bus bar furnished with it which is bonded to the #10 wire you ran through the nipple which wire is bonded to (you screwed it to) the ground bus bar in the main panel which is bonded to the main panel frame. Ergo the subpanel is now grounded to the main panel. According to NEC 250.122, circuits breakered at 30 to 60 amps use a #10 ground wire.
But, that method leaves the 1 1/2" nipple without an approved bond to ground, assuming it is installed in concentric knockouts that are larger than 1 1/2". IF both knockouts are a maximum of 1 1/2", each end of the nipple would require a grounding locknut. Grounding/bonding bushings and grounding locknuts are slightly different then standard locknuts and bushings.

1 1/2 Inch Grounding Locknut - ARLGL150 | Wholesale Electrical Supply Company

1 1/2 Inch Grounding Bushing - ARL454 | Wholesale Electrical Supply Company
 
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