Sharing a EGC between two circuits

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Old 09-17-11, 12:10 PM
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Sharing a EGC between two circuits

I have read before that the ground can be shared between circuits run in conduit, but was wondering about when they are different sizes and different voltages. I think that you have to run the largest egc to accommodate the biggest circuit, but wasn't 100% sure. Example, 3/4" conduit carrying one 12g 110v circuit and one 10ga 220v circuit. Should this conduit be filled with 3 10ga wires (egc, 2 hots) and 2 12ga wires (hot and neutral)?
 
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Old 09-17-11, 12:33 PM
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Correct, the EGC is sized for the largest overcurrent circuit size.
 
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Old 09-18-11, 12:55 PM
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Thanks Boss ;-) . .
 
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Old 09-18-11, 10:20 PM
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Also, at the steel box, would you be required to ground the box with #8 or would a 12ga pigtail suffice? Would be pretty hard to get two #8's and two #12's under a twist nut.
 
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Old 09-19-11, 12:23 AM
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Since #10 conductors may not be protected at any higher than 30 amperes it is not necessary to have the equipment ground any larger than #10. In this case you would use a #10 bonding jumper to the metallic box.
 
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Old 09-19-11, 10:35 AM
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You can use a crimp on ring terminal to the box screw if the wire doesn't fit under the screw.
 
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Old 09-19-11, 08:19 PM
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Sorry I wasn't clear on the pigtail, it would be a crimp on ring terminal and I was referring to "under a twist nut" having to wire nut together two 10ga and two 12 gauge wires - I mistyped in the 8ga b/c I was thinking of the load carrying conductor.

Ultimately though, Furd, your saying that the box grounding is serviced by the size required by the amperage of that circuit. So on a 50a recep, that steel box is grounded with a #10, a 20a box would get grounded with a 14g or 12g conductor.
 
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Old 09-20-11, 10:10 AM
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Size the ground to the largest circuit in the box or conduit:

15A circuit = #14 copper ground
20A = #12
21A - 60A = #10
61A - 100A = #8
 
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Old 09-20-11, 11:35 AM
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And while you will probably never be involved in such a circuit a 200 ampere circuit (normally requiring 3/0 copper conductors) requires only a #6 (copper) equipment ground.
 
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Old 09-20-11, 08:17 PM
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Thanks Ben & Furd, much appreciated. Being able to land multiple ground wires (with ring terminals) under one screw in the box will be a huge help.
 
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