point of connection [RE-wrenches]

[Howie Michaelson]

Is it not the case that if it is acceptable to derate the main breaker on
the house panel, that you could backfeed a higher amount into the panel
(all breakers feeding the buss bar cannot add up to more than 120% of the
buss bar rating)?

Howie
--
Howie Michaelson
NABCEP Certified Solar PV Installer™

Sun Catcher, LLC
Renewable Energy Systems Sales and Service
VT Solar & Wind Incentive Program Partner
http://www.SunCatcherVT.com
(cell) 802-272-0004
(home) 802-439-6096


On Sat, May 3, 2008 11:22 am, Mark Frye wrote:
>
> NEC 2005
>
> 690.8 Circuit Sizing and Current
>
> (A) Calculation of Maximum Circuit Current. The maximum current for the
> specific circuit shall be calculated in accordance with 690.8(A)(1)
> through
> (A)(4)....
>
> ....(3) Inverter Output Circuit Current. The maximum current shall be the
> inverter continuous output current rating.....
>
> (B) Ampacity and Overcurrent Device Ratings. Photovoltaic system currents
> shall be considered to be continuous.
>
> (1) Sizing of Conductors and Overcurrent Devices. The circuit conductors
> and
> overcurrent devices shall be sized to carry not less than 125 percent of
> the
> maximum currents as calculated in 690.8(A)...........
>
> David, the Code is set up to force you to size to the inverter rated
> output,
> not the actual power delivered.
>
> I believe the thinking is that you may only have half the PV installed now
> so the small breaker would "work", but someone else might add more PV
> later
> without upsizing the conductor and breaker and that would be a problem.
>
> Mark Frye
> Berkeley Solar Electric Systems
> 271 Vistamont Dr
> Grass Valley CA 95945
> (530) 401-8024
> www.berkeleysolar.com
>
> -----Original Message-----
> From: David Buckner [mailto:dbuckner at solaresystems.com]
> Sent: Saturday, May 03, 2008 6:32 AM
> To: RE-wrenches at topica.com
> Subject: RE: point of connection [RE-wrenches]
>
>
> Wrenches,
> If Larry's line side service connection, even with its closer proximity,
> becomes costlier than the potential load side connection, could he feed a
> subpanel with the two 30A PV input breakers, then feed into the house MDP
> with a 40A breaker from this subpanel?  This would require calculations of
> DC input and resulting max AC output of the inverters.  If the inverters
> won't ever be putting out 20A anyway, then the 40A (continuous duty?)
> breaker shouldn't be tripping and code would be met?  I'm asking, not
> telling.  Larry, what is the DC STC input anyway?
>
> David
>
>
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>


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