Electrical – Determining Bus-Bar Rating for PV Installation

electricalelectrical-panelinvertersolar-panels

I already have a primary PV inverter connected up through a 40A breaker. I'm looking to expand by adding a second PV inverter. To comply with the 2014 NEC 705.12(D)(2) rule I need to know the panel bus bar rating. The existing system drawings were done based on the assumption that the main breaker and the bus bar were rated equivalently (at 200A_, but if I'm reading the label in the panel correctly, the bus bar is rated at 225A.

If the bus bar is indeed rated at 225A then my allowance under the NEC rule is 1.2*225 = 270 – 200 (main breaker) = 70A. With the existing system taking up 40A, then I could install another 30A breaker for the second inverter. If not I'd have to replace the main breaker with a 175A breaker.

I have partial picture of the sticker inside the panel, and realized it matched a sample from a data sheet, so I'm including the data sheet picture.

panel data sheet rating label

Am I reading the "Mains 225A max" as meaning that the bus bar is rated at 225A?

Best Answer

Originally I was wondering if the Mains 225A max. from the label inside the panel box was the rating of the bus bar. Since it seems there are/can be addition labels on the panel interior itself (the black plastic holding the breakers and bus bars), I wasn't sure if I'd have to pull the meter and main breaker to confirm.

Researching Schneider's website, I noted that for 42-space single phase interiors in QO plug-on neutral style there appear currently to only be 225A bus bar ratings available for purchase. While that seems to be a pretty good indicator, I still wanted to confirm a bit more if possible.

I contacted Schneider's technical support to ask if they could confirm that they've only ever sold 225A bus bar interiors for the style/size/phase of my box. The representative wasn't able to do that. But representative proceeded to say in our chat:

But if you look at the wiring diagram label (should be on the inside of the box on the right or left endwall), it will have a rating along the lines of "Mains max" or somewhere along those lines. That will give you the rating of the bus. It is most likely 225 A, but I can't say for sure without knowing the actual part number

So it appears that you can determine the bus bar rating from the panel box interior label without needing to find a label on the breaker holding interior itself.

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