[RE-wrenches] 120% rule applying to conductors

[Kristopher Schmid]

It seems to me that the conductor should not be subject to the 120% rule
despite what the code says.  The potential safety issue here is overloading
the neutral bus, right?  While feeding currents could be additive in the
panel, they would be subtractive on the feeder, no?  I seem to remember
seeing this discussion on the list before.

Kris

On Fri, Sep 28, 2012 at 8:26 AM, Aaron Mandelkorn <reosolar at gmail.com>wrote:

> I agree.  With a 150A bus being fed by 100A from the grid leaves 80
> additional amps (120% of 150A) to feed the bus from outside sources.  It
> seems to me that 40A of PV being back fed will be just fine.
>
> Aaron Mandelkorn
> NABCEP Certified PV Installer
> Renewable Energy Outfitters
> Box 65 Salida, CO. 81201
> (970)596-3744
> reosolar at gmail.com
> www.reosolar.com
>
>
>
>
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>
>
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>
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>
>
> On Sep 28, 2012, at 6:32 AM, Drake wrote:
>
>  Are you sure you can't?  Since the bus has a rating of 150 A and is
> protected by a 100 A breaker, there is plenty of room to not over amp the
> bus from the two sources of power.
>
> The amperage from the inverter will cancel amperage coming from the
> utility in the feeder.  The wire will never supply over the 100 A.  The
> theoretical max the inverter could backfeed would be 40 Amps in the 100 Amp
> cable if no loads were being supplied.  It would certainly not be a safety
> issue.  Am I missing something in the code?
>
>
> At 12:51 AM 9/28/2012, you wrote:
>
> Mac:
>
> Nope.
>
>
> William Miller
>
> PS:  It's pretty straight forwards, the code says "bus or conductor."
>
> wm
>
> PPS:
>
> Can  you customer live with a smaller feeder breaker, say 125 amps?  If
> so, your gold.
>
> wm
>
>
>
> At 06:43 PM 9/27/2012, you wrote:
>
> Hello wrenches,
>
> I am looking for advice on how the 120% rule applies to feeders for a
> subpanel.  I have this scenario:
> 150A bus rating on subpanel with main breaker of 100A.  The conductors
> feeding this subpanel are 100A rated conductors.  Can I backfeed with a 40A
> breaker?
>
> Thanks
>
> --
>
>
>
> Mac Lewis
>
> *"Yo solo sé que no sé nada." -Sócrates
> *
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-- 
Shine On!

Kris Schmid
Legacy Solar, LLC
864 Clam Falls Trail
Frederic, WI 54837
www.legacysolar.com
715-653-4295
NABCEP Certified PV Installer
BSEE
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