Working on a 45 kW PV system with residential 120/240 AC backfeed. The customer has a Square D 600 A I-line MDP that is LUG FED from the meter and there are currently 5 breakers being used as 5 main service disconnects in this panel (below the six switch rule). There is currently one available breaker slot not being used. Total output from all of my inverters combined requires a 225 A breaker. I have confirmed with Schneider/Square D that the max breaker size they allow in any of the two pole breaker slots in their I-line panels is 225 A when the service voltage is at or below 240 V. Currently there are three 200 A breakers and two 150 A breakers each feeding different loads panels. (Its a very large house!)
My question is if I were to put a 225 A breaker onto this panel is this considered a backfed breaker that must conform to the 120% rule or is this a supply-side connection? I am thinking this is technically a supply-side connection since there is no main breaker and the busbar is technically part of the main service conductors feeding the 5 main service breakers. Therefore the 120% rule shouldn't apply, right? I really don't see any difference electrically speaking if we connect with the 225 A breaker at the busbar vs. doing a supply side connection on the service conductors outside. Either way this busbar is still fed with both the utility power and solar power to the main lugs.
705.12(A) says that we can do a supply side connection as long as we don't exceed the rating of the service, which we're well under with 225 A of backfeed on a 600 A service. For 705.12(D)(2)(1 & 2) I'm not making any connections to feeders since all the main service disconnects are technically after the point of my backfeed, so that section doesn't apply. And for 705.12(D)(2)(3) since there is no main overcurrent device protection the busbar portion of the service conductors in the MDP the 120% calculation shouldn't apply.
From what I'm seeing this is a supply side connection and I should be all on the up and up with code to make a connection in this MDP with a 225 A breaker but I'm curious what you all think. Am I good to do a breaker in this MDP for my solar backfeed or are there some additional rules I'm violating that I'm not aware of?
Side question, if I do install the 225 A breaker should this be located at the opposite end of the MDP busbar from the main lug connection or does it even matter? Also, technically this breaker would not count as one of 6 service disconnect since you can still disconnect all of the loads panels with the 5 service breakers in the MDP, right?
My question is if I were to put a 225 A breaker onto this panel is this considered a backfed breaker that must conform to the 120% rule or is this a supply-side connection? I am thinking this is technically a supply-side connection since there is no main breaker and the busbar is technically part of the main service conductors feeding the 5 main service breakers. Therefore the 120% rule shouldn't apply, right? I really don't see any difference electrically speaking if we connect with the 225 A breaker at the busbar vs. doing a supply side connection on the service conductors outside. Either way this busbar is still fed with both the utility power and solar power to the main lugs.
705.12(A) says that we can do a supply side connection as long as we don't exceed the rating of the service, which we're well under with 225 A of backfeed on a 600 A service. For 705.12(D)(2)(1 & 2) I'm not making any connections to feeders since all the main service disconnects are technically after the point of my backfeed, so that section doesn't apply. And for 705.12(D)(2)(3) since there is no main overcurrent device protection the busbar portion of the service conductors in the MDP the 120% calculation shouldn't apply.
From what I'm seeing this is a supply side connection and I should be all on the up and up with code to make a connection in this MDP with a 225 A breaker but I'm curious what you all think. Am I good to do a breaker in this MDP for my solar backfeed or are there some additional rules I'm violating that I'm not aware of?
Side question, if I do install the 225 A breaker should this be located at the opposite end of the MDP busbar from the main lug connection or does it even matter? Also, technically this breaker would not count as one of 6 service disconnect since you can still disconnect all of the loads panels with the 5 service breakers in the MDP, right?
) said, you really need to go over this design with your AHJ. Some AHJ's will not let you land a backfed PV breaker in an MLO MDP no matter what the size or handle count is. For example, here in Austin when I encountered a very similar situation, they directed me to mount a bladed fused disco on the wall and tap the busbars of the MLO MDP with conductors less than 10' long.