[RE-wrenches] Conductor Sizing for Supply Side Connection

[Garrison Riegel]

Thanks Allen for clarifying why a 60A is required.  I was wondering.  The
spec does list a surge current of 9000W so I thought that may be the
rationale, but even that would only require a 50A, and since this surge
occurs during 'stand-alone mode' it didn't seem to apply to the OCPD at the
main panel.  Your explanation makes more sense, but I wonder why then they
don't list the AC input breaker size as 60A max.  If you have few backup
loads, and are not on the 2011 NEC, a 40A could theoretically be fine?

 

Thanks all for your thoughts, much appreciated.

 

Garrison

 

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan
Sindelar
Sent: Wednesday, February 27, 2013 6:08 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Conductor Sizing for Supply Side Connection

 

August,
The 60A breaker is intended to allow grid power to pass through to the loads
in excess of the inverter's stand-alone output. The point of 705.12 (moved
in the 2011 NEC from 690.64 (B)(2)) is to differentiate between load
pass-through current and sell current. The amount of current fed into the
grid is (4500/230 =) 19.56A, while the amount that can be taken from the
grid and passed through to the load is much greater. If you were limited to
a 40A breaker in order to maintain 120% of a 200A main bus, you'd be prone
to nuisance trips under large cumulative loads.

Allan

Allan Sindelar
 <mailto:Allan at positiveenergysolar.com> Allan at positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
Positive Energy, Inc.
3209 Richards Lane (note new address)
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com <http://www.positiveenergysolar.com/>  

 

 

 

 

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