L6-20P -> L6-30R

Seth Mattinen sethm at rollernet.us
Wed Mar 19 21:51:54 UTC 2014


On 3/19/14, 10:21, Jay Ashworth wrote:
> It is exactly that: no one says you*can't*  wire a 20A branch circuit with
> #10.
>
> It is even*possible*, though unlikely, that if you did so, you wouldn't
> have to derate it to 80%.  I would have to reread the Code to be sure.

Well, I'd say it's pretty likely. However highly unlikely to be 
code-worthy of slapping on a 30A breaker in place of a 20. 10-20 CCCs in 
a raceway or cable is a 50% derating, so if those conductors were for 
20A branch circuits it would have to be 10AWG, not 12 since with 10AWG 
you're derating from 40A. But the max protective device on 10AWG is 30A 
unless permitted by 240.4.

Even 7-9 CCCs in a raceway or cable derates 10AWG to 28A (70%), so while 
still suitable for a 20A breaker it's not for 30A. Max would be 6 CCCs 
to stay at 80% derating (4-6 CCCs).

~Seth



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