[169895] in North American Network Operators' Group
Re: L6-20P -> L6-30R
daemon@ATHENA.MIT.EDU (Rob Seastrom)
Wed Mar 19 18:33:41 2014
To: Jay Ashworth <jra@baylink.com>
From: Rob Seastrom <rs@seastrom.com>
Date: Wed, 19 Mar 2014 18:33:18 -0400
In-Reply-To: <21771767.12127.1395249665075.JavaMail.root@benjamin.baylink.com> (Jay
Ashworth's message of "Wed, 19 Mar 2014 13:21:05 -0400 (EDT)")
Cc: nanog@nanog.org, rs@seastrom.com
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Jay Ashworth <jra@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%.
http://cliffordpower.com/wp/wp-content/uploads/2010/08/CPS_info_sheet_37_CB_80_versus_100.pdf
-r
