We have a PV System with 6 strings of Enphase microinverters connected to a 208v/Ph combiner panel with a 150a main breaker, this panel connects to a fused AC disconnect fused at 80a. Then this connects to an 80a back feed breaker in the main 400a panel. Max system AC current is 63a at 208v/3Ph. The electrical contractor is saying we need to change the 150 main breaker in the combiner panel due to this being against code. Has not said what code. It is my understanding that this 150a main breaker does not need to be changed. It is mearly a 150a rated switch to shut down all 6 strings at once. Thoughts?
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PV AC Combiner Main Breaker
- Thread starter vargo320
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ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
We have a PV System with 6 strings of Enphase microinverters connected to a 208v/Ph combiner panel with a 150a main breaker, this panel connects to a fused AC disconnect fused at 80a. Then this connects to an 80a back feed breaker in the main 400a panel. Max system AC current is 63a at 208v/3Ph. The electrical contractor is saying we need to change the 150 main breaker in the combiner panel due to this being against code. Has not said what code. It is my understanding that this 150a main breaker does not need to be changed. It is mearly a 150a rated switch to shut down all 6 strings at once. Thoughts?
You don't need a main breaker in the AC combiner or a fused disconnect. An MLO AC combiner and an unfused disco are sufficient; the 80A backfed breaker in the main is all the OCPD you need. BTW, your conductors from the MDP to the AC combiner have to have a conditions of use ampacity greater than 70A.
Technically, if you are under the 2011 code or earlier, the 150A main breaker in the AC combiner contributes to the 120% rule; that may be what the contractor is objecting to, but realistically those busbars are protected at 80A by the breaker in the MDP. I would just remove the main breaker in that panel.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Yes, as long as the ratings of all the breakers in the panel, both supply and load, excluding the main breaker, do not sum to more than the rating of the panel bus. See 705.12(D)(2)(3)(c).We are in NY and under NEC 2014. So basically we can keep the 150a main in the combiner panel and be to code, correct?
Maybe something particular to the local flavor of the electrical code but there is nothing in the 2014 NEC that should require you to change the 150A CB assuming the bus rating is 150A or greater. I would have them point out where in the NEC it is required, they might still be thinking of the 2011 code.
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