[RE-wrenches] conductors and the 120% rule

[Jason Szumlanski]

Yeah, I assumed you meant the four conductors. The exception would solve
your problem if it's physically possible.

How long of a run are we talking about? The cost difference shouldn't be
bad for a short distance.


Jason Szumlansk
i

Fafco Solar



On Tue, Mar 4, 2014 at 3:34 PM, Kirk Herander <kirk at vtsolar.com> wrote:

> Whether or not a further derate has to be applied is the killer here, as I
> am working with existing panels and conductors. In an old Code
> Corner(HP140) J. Wiles goes through a similar scenario and calls out the
> allowable current rating and conductor in 310.15, but makes no mention of
> applying additional derate factors. The .8 derate for 4-6
> conductors(l1,l2,l3, & n) will put the existing 4/0 cable between feed-in
> and main panel at 208 amps, less than the allowable 217. I'd hate to need
> to upsize the wire to 250 mcm.
>
>
>
> Kirk Herander
>
> VT Solar, LLC
>
> dba Vermont Solar Engineering
>
> NABCEPTM Certified Inaugural Certificant
>
> NYSERDA-eligible Installer
>
> VT RE Incentive Program Partner
>
> 802.863.1202
>
>
>
> *From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
> re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Jason Szumlanski
> *Sent:* Tuesday, March 04, 2014 2:57 PM
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] conductors and the 120% rule
>
>
>
> 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
>
>
>
>
> [image: Description: Image removed by sender.]
>
>
>
> 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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