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EGC size for 20A MWBC when up sizing feed for voltage drop

mike93lx

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On 2015 code cycle.

I am upsizing a 20a MWBC to #10 THWN due to distance. Do I need a #10 egc or is #12 sufficient? The cost difference is not significant, so I may run 10 anyway, but curious on options.

Thanks
 
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wyliesdiesels

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circuits using 14/12/10 for minimum size will always have the same size EGC when you upsize the wire due to VD or temp adj.... if the circuit is larger, say 40a, then the EGC might be smaller than the ungrounded conductors even when upsizing for VD because the EGC is smaller to begin with...
 
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mike93lx

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circuits using 14/12/10 for minimum size will always have the same size EGC when you upsize the wire due to VD or temp adj.... if the circuit is larger, say 40a, then the EGC might be smaller than the ungrounded conductors even when upsizing for VD because the EGC is smaller to begin with...
So if this was a bigger circuit, say a 60a, and one used #2 AL because it was on hand, can a egc smaller than 4 be used? Or is the reason for the up size irrelevant?
 
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wyliesdiesels

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So if this was a bigger circuit, say a 60a, and one used #2 AL because it was on hand, can a egc smaller than 4 be used? Or is the reason for the up size irrelevant?
the reason is irrelevant. code requires the EGC to be increased proportionally when the ungrounded conductors are increased in size.

unfortunately for the scenario you brought up, #4 is the min req for the EGC. actually #5 could work since #6 is just slightly too small however #5 doesnt exist as a single conductor on a roll....
 
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mike93lx

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the reason is irrelevant. code requires the EGC to be increased proportionally when the ungrounded conductors are increased in size.

unfortunately for the scenario you brought up, #4 is the min req for the EGC. actually #5 could work since #6 is just slightly too small however #5 doesnt exist....
Thanks, that is what I expected.

I didn't think the reason for upsizing was relevant and wanted to confirm.
 

pattenp

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Thanks.

What if the VD was in the recommended range and I was just upsizing because I hated money/had the wire on hand? Just a hypothetical
I should have been clearer. Wylie covered it that whenever the current carrying conductors are upsized beyond what's needed the ground conductor also needs to be upsized an equal percentage amount. Old code verbiage was just for when upsized for voltage drop.
 
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