Interconnection question for 17 kw solar


Solar Designer
I am designing a System 17 KW with micro inverters IQ 7 PLUS, BACK FEED IS 7O A, the main service panel is 200/200 Pedestal type. The main service panel has 100A Breaker feeding sub ( this sub panel is rated 150A with main disconnect 150A) and the lugs are fed by another 125A MLO sub panel ( which has under 100A Loads) plus one 20A DPB and one 15A SPB. (Total breaker plus feed load=100+100+15+20=235< 200*1.2<=240)

Now my question is Can i derate the 150A Sub Panel breaker to 100A, SO THAT ACCORDING TO 120 PERCENT RULE (1.2*150-100=80A backfeed).is still valid.
but the main service panel is still 200/200 and has only 40A Backfeed. is it code complaint per NEC.

second questions if the above logic is untrue can I do GMA ( generation meter adapter ) provided by POCO ( southern california edison) for pedestal panel which is outside the mobile home. ( most of the GMA ARE DONE ONLY FOR BOTTOM FED TYPE AND MAIN METER COMBO ONLY )

3rd question can we do 400A upgrade with 200/200 split bus bar for pedestal panel. THIS SOLUTION IS MY Last choice if allowed.

i will really appreciate the answers. thank you


Senior Member
Unless you are otherwise taking advantage of the 2020 NEC's 705.13 to control the system current relative to loads, the 705.12 busbar protection rules propagate to upstream panelboards, all the way from the point of interconnection to the service point. If you interconnect on a subpanel per the 120% rule, assume the worst case scenario that all of its local load may diminish to zero. The full inverter output current then propagates to the main panel from which the subpanel is supplied. You'll now need to follow a busbar protection rule there as well. Not necessarily the 120% rule in both places, but one of the 705.12 busbar protection rules for each panel, nevertheless.

As for downsizing a main breaker in order to comply with the 120% rule, the NEC requires that you have facts to back it up. Such as a revisited load calculation, or 15-minute demand interval data for 30 days from either your own meter or the utility's records.