AC Service Panel max Solar Backfeed

DaveF

Hello,

Newbie here. I plan to add solar to my home and have a question about how many amps I can backfeed into my AC service panel using Net Metering. I know the NEC limits this to 120% of the service panel busbar capacity minus the main circuit breaker rating.

I have an old GE panel from the ‘70s, Model number TM1410MUF that has a 100A main breaker, so at first glance it looks like I can only have a 20A solar breaker. But, the label on the door says “Main Ratings 120/240V A-C  3—WIRE”, then below that it says “125A Max SEE MAIN CIR. BKR. RATING”.

Is this my busbar rating, and so would I be able to install a solar breaker (1.2 x 125) – 100 Main = 50A? Note I only need 30-40A.

Thanks!

Dave Angelini

20 A  max on a 100 amp panel.  40 A max on a 200 A panel.

DaveF

Thanks, that's a great rule of thumb but not the whole story. For instance, I could put an 80A main breaker in a 100A panel and backfeed 40A of solar and meet NEC 705.12 (D) (3). But I of course don't want to do that. I'd like to keep my 100A main and backfeed 40A solar. 

I know the viability of doing this is based on the buss bar capacity of the panel and I think the note on the label is telling me it is rated for 125A, even though it has a 100A breaker. But I'm not sure...

Dave Angelini

You would never get a permit for that and that us what counts.