L6-20P -> L6-30R

Rob Seastrom rs at seastrom.com
Wed Mar 19 22:33:18 UTC 2014

Jay Ashworth <jra at baylink.com> writes:

> 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.

It's not the conductor that you're derating; it's the breaker.  Per
NEC Table 310.16, ampacity of #12 copper THHN/THWN2 (which is almost
certainly what you're pulling) with 3 conductors in a conduit is 30
amps.  Refer to Table 310.15(B)(2)(a) for derating of more than 3
current-carrying conductors in a conduit.  4-6 is 80%, 7-9 is 70%.
Plenty good for 20 amps for any conceivable number of conductors in a
datacenter whip.

Thermal breakers are typically deployed in an 80% application for
continuous loads, per NEC 384-16(c).  See the references to 125% of
continuous load, which of course is the reciprocal of 80%.



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