point of connection [RE-wrenches]

[Mark Frye]

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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