Paul Donehue
Member
- Location
- San Jose, CA
Hello folks, this is my first post. Been reading the forum for some time, some great information.
Im in the planning stage of a microinverter based system (Silfab 310 modules, enphase 7+ microinverters, and Ironridge racking).
Im having some kinks in my planning due to a somewhat unusual main service panel with feedthrough lugs. Seems the NEC code is a little vague for this setup.
I have a 200A main combination panel with feedthru lugs that feeds a 200A main breaker subpanel in my garage. The service panel basically feeds through to the panel in the garage that feeds all the primary house loads.
I'd like to add a 60A PV system and would like to leverage the 120% rule if at all possible so that I only have to downsize to 175A main breaker to allow for future expansion.
The main service entrance panel has a 50A breaker to an outlet for a compresser/portable equipment as the only load but I am considering future addition of 100A breaker to the main panel to feed an ADU.
After reading the forum I found several old posts that seemed to offer conflicting information on how to consider the feedthrough lugs and attached panel for purposes of NEC 705.12 (b) (3)
1) Some of the posts suggested that by placing the backfeed inverter into the panel furthest from the main breaker would meet (b) 120% rule. However the feedthrough lugs are at the end of the busbar, while not a physical breaker seems to violate the spirit of the code.
2) Some other posts suggested that the (c) sum of breakers in subpanel might apply and the lugs are not considered a breaker in this panel for purposes of the calculation. The argument being that the feed lugs are characterized separately by the panel manufacturer and technically not part of the bus.
3) The other option I was thinking of is to backfeed the solar into the furthest slot away from the main breaker of the subpanel in the garage and derate the service panel and subpanel breakers to 175A. For this scenario the 120% rule (b) would work for the subpanel in the garage but then when I carry this upstream to the main panel I would then possibly face challenge as there are not really any load breakers other than the 50A compressor in the main panel. It seems to expose the possibility the inspector might say that (b) implies that there are breakers present to spread out the loading which was the basis for the 120% rule. If I did add more breakers in the future then there would be some spreading of the current but it seems it comes to luck of the draw with the inspectors.
Also for scenario 3, since I would no longer have the PV feeback breaker in the main panel, I would not have a solar disconnect within 10' of the main panel. The AHJ seemed ok with only having the A/C disconnect in the garage, but Im afraid PGE might make me have the A/C shutoff within 10' of the meter. If I wanted to install an AC shutoff, then it seems PGE wants it within 10' of the main panel. This would require looped the PV through an AC shutoff placed near the main and then back to feed the subpanel in the garage. This does not seem elegant and the extra detouring might present challenges meeting voltage rise.
PGE has a document that shows scenario for when A/C shutoff is needed online, and my system seems to meet the criteria (no line side tap, no 3 phase, < 320A) but Im not sure if they are assuming central inverter based system, or might insist that I have it despite the "AC Disconnect and Variance Logic Standard NEM" document that says its not needed.
Im thinking I might need to bite the bullet and downgrade my system to 50A and downside main breaker to 150A but this does not leave any room for future expansion.
I would greatly appreciate any help in navigating my possible options and feedback on what you folks would do in my situation.
Thanks,
Kuma
Im in the planning stage of a microinverter based system (Silfab 310 modules, enphase 7+ microinverters, and Ironridge racking).
Im having some kinks in my planning due to a somewhat unusual main service panel with feedthrough lugs. Seems the NEC code is a little vague for this setup.
I have a 200A main combination panel with feedthru lugs that feeds a 200A main breaker subpanel in my garage. The service panel basically feeds through to the panel in the garage that feeds all the primary house loads.
I'd like to add a 60A PV system and would like to leverage the 120% rule if at all possible so that I only have to downsize to 175A main breaker to allow for future expansion.
The main service entrance panel has a 50A breaker to an outlet for a compresser/portable equipment as the only load but I am considering future addition of 100A breaker to the main panel to feed an ADU.
After reading the forum I found several old posts that seemed to offer conflicting information on how to consider the feedthrough lugs and attached panel for purposes of NEC 705.12 (b) (3)
1) Some of the posts suggested that by placing the backfeed inverter into the panel furthest from the main breaker would meet (b) 120% rule. However the feedthrough lugs are at the end of the busbar, while not a physical breaker seems to violate the spirit of the code.
2) Some other posts suggested that the (c) sum of breakers in subpanel might apply and the lugs are not considered a breaker in this panel for purposes of the calculation. The argument being that the feed lugs are characterized separately by the panel manufacturer and technically not part of the bus.
3) The other option I was thinking of is to backfeed the solar into the furthest slot away from the main breaker of the subpanel in the garage and derate the service panel and subpanel breakers to 175A. For this scenario the 120% rule (b) would work for the subpanel in the garage but then when I carry this upstream to the main panel I would then possibly face challenge as there are not really any load breakers other than the 50A compressor in the main panel. It seems to expose the possibility the inspector might say that (b) implies that there are breakers present to spread out the loading which was the basis for the 120% rule. If I did add more breakers in the future then there would be some spreading of the current but it seems it comes to luck of the draw with the inspectors.
Also for scenario 3, since I would no longer have the PV feeback breaker in the main panel, I would not have a solar disconnect within 10' of the main panel. The AHJ seemed ok with only having the A/C disconnect in the garage, but Im afraid PGE might make me have the A/C shutoff within 10' of the meter. If I wanted to install an AC shutoff, then it seems PGE wants it within 10' of the main panel. This would require looped the PV through an AC shutoff placed near the main and then back to feed the subpanel in the garage. This does not seem elegant and the extra detouring might present challenges meeting voltage rise.
PGE has a document that shows scenario for when A/C shutoff is needed online, and my system seems to meet the criteria (no line side tap, no 3 phase, < 320A) but Im not sure if they are assuming central inverter based system, or might insist that I have it despite the "AC Disconnect and Variance Logic Standard NEM" document that says its not needed.
Im thinking I might need to bite the bullet and downgrade my system to 50A and downside main breaker to 150A but this does not leave any room for future expansion.
I would greatly appreciate any help in navigating my possible options and feedback on what you folks would do in my situation.
Thanks,
Kuma