[RE-wrenches] conductors and the 120% rule

[Jason Szumlanski]

Both the bus and conductors need to be rated for 217 amps minimum. As you
mentioned, the bus is not a problem. The way I interpret it, the conductor
size required would be after derate factors are applied. The rating of the
conductor is ultimately dependent on the derate factors.

If you can locate your subpanel adjacent to the main distribution panel,
you may be able to use Exception #3 to 310.15(B)(2) by connecting the
panels with a short nipple. I assume you are just looking at a number of
conductor derate and not an ambient temperature derate.

Jason Szumlanski

Fafco Solar





On Tue, Mar 4, 2014 at 12:05 PM, Kirk Herander <kirk at vtsolar.com> wrote:

> Hello,
>
> I have a 225 amp 3-phase main lug sub-panel protected by a 200 amp
> breaker. My inverter breaker feeding the sub panel is 60 amps. So 225 a bus
> x 1.2 = 270 amps. That's less than the sum of the two breakers of 260 amps,
> so no issue there. The conductors between sub and main panel have to be
> rated for at least 260/1.2 = 217 amps, correct? Is this 217 amps before or
> after derating the conductor?
>
>
>
>
>
> Kirk Herander
>
> VT Solar, LLC
>
> dba Vermont Solar Engineering
>
> NABCEPTM Certified Inaugural Certificant
>
> NYSERDA-eligible Installer
>
> VT RE Incentive Program Partner
>
> 802.863.1202
>
>
>
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