[RE-wrenches] sizing a sub-panel used to combine multiple inverter outputs

[Al Frishman]

Hi Wrenchers,

When using a sub-panel for the sole purpose of combining the output of
multiple single phase inverters does NEC 690.64 (B) (2) apply?  I know that
this topic has been discussed but I am still not clear.

 

The "Can we Land" Article pg 11 Diagram 2b shows that using a Subpanel
eliminates the problem of exceeding the 120% rule illustrated in diagram 2a
but it does not show the rating of the sub-panel.    In the example it shows
3 Fronius 7500W single phase inverters landing in a sub-panel and then the
3-phase sub-panel grid connected to a 80A 3-phase breaker in a 400A main
panel.    What is the minimum Amp rating required for the 3-phase Sub-panel
in diagram 2b?  Do we only need to size it for the OCP for the combined
outputs of the 3 inverters (80A) or do the three 50A two-pole breakers need
to be considered? 

 

For easy reference here is a link to the article:
http://www.spgsolar.com/wp-content/uploads/2010/05/SPGLeBlancYates.pdf

 

All feedback is appreciated.

 

Al Frishman
AeonSolar

(917) 699-6641 - cell
(888) 460-2867
 <http://www.aeonsolar.com/> www.aeonsolar.com

 

 

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