Not answering your question, but does each unit have its own meter and service conductors? If not, you may have a 705.12 issue in the MDP that feeds the subpanels.Working in CA on a new multi-family dwelling unit building. Does the CEC require Arc-fault breakers for microinverter circuits?
We ran NM cable from roof array to each units sub-panel.
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Thanks, guys!As of right now (2020 NEC, 2022 CEC), arc fault protection is only required for 120V circuits that supply outlets in certain rooms inside the building. So your circuits are exempt.
What was that code section though? I can't remember, it was in an odd place.As of right now (2020 NEC, 2022 CEC), arc fault protection is only required for 120V circuits that supply outlets in certain rooms inside the building. So your circuits are exempt.
Thanks, I did not go back far enough. It was an interesting story about how this got into the code. It's one of those stories about how the code can be manipulated to create a market for a device that otherwise would not be used.I think it was only in the 2014 NEC, in 705.
Edit: It was 705.12(D)(6).
I will shut up about it, but understand that 705.12(B)(3) has to be complied with in every panel all the way back to the utility meter. If you have PV going into a bunch of subpanels downstream from an MDP, it appears to me that your only avenue of compliance in the MDP will be 705.12(B)(3)(3), i.e., sizing the MDP such that the rating of the busbars is equal to or greater than the sum of the ratings of all the breakers connected to them. You cannot use 705.12 (B)3)(2), i.e., the 120% rule, because the PV output cannot all be entering the MDP at the opposite end of the busbars from the utility feed.I ask again: does each unit have its own meter and service conductors, or are all the units supplied by subpanels fed from a single MDP? If the latter, how are you addressing 705.12(B)(3) in the MDP?
In the situation you describe, if there are more than a few units, I would think that 705.12(B)(3)(1) would often be the less demanding path to compliance. E.g. a 400A service to a panel with (6) 100A breakers to (6) units, each with 15A of microinverters. (B)(3)(3) would require a 600A busbar, while (B)(3)(1) would only require a 490A busbar.it appears to me that your only avenue of compliance in the MDP will be 705.12(B)(3)(3), i.e., sizing the MDP such that the rating of the busbars is equal to or greater than the sum of the ratings of all the breakers connected to them
Yes, that could work if there are only six units and if 15A is 1.25X the max inverter current. I tend to forget about that one because it only rarely applies to the systems I have designed. I only brought it up because sometimes people forget that 705.12(B)(3) applies all the way back to the meter.In the situation you describe, if there are more than a few units, I would think that 705.12(B)(3)(1) would often be the less demanding path to compliance. E.g. a 400A service to a panel with (6) 100A breakers to (6) units, each with 15A of microinverters. (B)(3)(3) would require a 600A busbar, while (B)(3)(1) would only require a 490A busbar.
Quite likely the 'MDP' is a meter bank with a service disconnect breaker for each meter, and it doesn't matter.I will shut up about it, but understand that 705.12(B)(3) has to be complied with in every panel all the way back to the utility meter. If you have PV going into a bunch of subpanels downstream from an MDP, it appears to me that your only avenue of compliance in the MDP will be 705.12(B)(3)(3), i.e., sizing the MDP such that the rating of the busbars is equal to or greater than the sum of the ratings of all the breakers connected to them. You cannot use 705.12 (B)3)(2), i.e., the 120% rule, because the PV output cannot all be entering the MDP at the opposite end of the busbars from the utility feed.
.. sometimes people forget that 705.12(B)(3) applies all the way back to the meter.
Usually they are together with nothing between them, but yes, I agree. My point was that sometimes people have the incorrect impression that 705.12(B) only applies in the panel that the PV is directly connected to.705.12(B) applies back to the service disconnect, regardless of where any meters are.
Yes, I see it all the time. Mostly because applying it to all the other panels in the path causes problems people just don't want to have to deal with. They know deep in their soul that it applies. ;-)Usually they are together with nothing between them, but yes, I agree. My point was that sometimes people have the incorrect impression that 705.12(B) only applies in the panel that the PV is directly connected to.
@ggunn, these are meter bank setups with a service disconnect for each unit, as jaggedben described here. These are 2, 3, and 4 unit dwellings.Quite likely the 'MDP' is a meter bank with a service disconnect breaker for each meter, and it doesn't matter.
