The oddity is that the NEC allows services without a main breaker. Such a service is clearly less protected than one with a main breaker. I'm not clear why this is allowed, but it is.Given that, a main breaker protected service is protected from overload by the main breaker and the calculation. The 120% rule on PV breakers addresses the possibility the additional source of power would undermine the protection from overload provided by the main breaker.On the other hand a MLO panel service with multiple breakers is only protected from overload by calculation. Adding PV breakers isn't going to reduce or undermine that protection, so there is no need for a 120% rule.Lastly, consider a service where the service lateral conductors enter a gutter with multiple "taps" to main breaker service panels. A PV disconnect with breaker is set next to these service panels and the PV conductors run to another tap in the gutter. This is definitely an acceptable arrangement with a line side PV connection, yes? This electrical arrangement of service conductors is identical to using a MLO panel instead of the gutter, the only difference is whether the conductors are individual wires or busbars.
Cheers, Wayne
The oddity is that the NEC allows services without a main breaker. Such a service is clearly less protected than one with a main breaker. I'm not clear why this is allowed, but it is. Given that, a main breaker protected service is protected from overload by the main breaker and the calculation. The 120% rule on PV breakers addresses the possibility the additional source of power would undermine the protection from overload provided by the main breaker.
On the other hand a MLO panel service with multiple breakers is only protected from overload by calculation. Adding PV breakers isn't going to reduce or undermine that protection, so there is no need for a 120% rule. Cheers, Wayne
I know I get it, In both of these situations service rating sized for calculated load.
In the main breaker panel the amount of allowable load side connected PV source normally is in the 20% range of the main breaker that is sized close to the buss rating of the panel current flow on the bus is based on the load. The amount of PV current is kept in check by the 20 % rule so if calculated load is ignored and a load is added to the bus that exceeds the service sizing design the most current support the increased load can get from the PV source would be in the 20% range . Current in both directions onto the buss around 80% from the utility and 20% from the PV source. When current on the buss reaches the range of 120% of the main breaker rating the main should open and current flow from both sources is interrupted.
.Lastly, consider a service where the service lateral conductors enter a gutter with multiple "taps" to main breaker service panels. A PV disconnect with breaker is set next to these service panels and the PV conductors run to another tap in the gutter. This is definitely an acceptable arrangement with a line side PV connection, yes? This electrical arrangement of service conductors is identical to using a MLO panel instead of the gutter, the only difference is whether the conductors are individual wires or busbars. Cheers, Wayne
Current flow is in one direction through the mains so each bus current is limited by the over current breaker ahead of the buss. The PV source contribution can equal the service rating. Line side connection rules seem to make the assumption that current flow will be in one direction to the distribution panels. The PV source current to the utility grid does not pass through load distribution equipment
On the other hand a MLO panel service with multiple breakers is only protected from overload by calculation. Adding PV breakers isn't going to reduce or undermine that protection, so there is no need for a 120% rule. Cheers, Wayne
But is also unique when defined as a line side connection. The line side PV source connection point directly to the buss being the only circumstance on a line side connection current flow is in both directions on the buss. No code mandated guidelines to where the PV source breakers should be installed on the buss. Perhaps if the PV source was tied to the middle of the buss it would make little difference or to the top of the buss close to the main lugs.
100 Amp main lug panel 100 amp service.
We supply 100 amp buss in a panel with 100 amps of PV source line side rules limitation, in the middle of the panels buss.
We have a pretty constant current flowing to the utility grid on the 100 amp rated buss , perhaps in the 100 amp range, the buss is supplying calculated load, the difference I see the PV current on the buss is not just flowing toward calculated load it is also flowing toward the utility grid load. by the line side load rules it could be 100 amps only limited by the service rating size.
I do not claim to be an expert as you guys may be, so maybe all this doesn’t matter, it just that the line side connection rules didn’t seem like they were intending for that much PV current to be flowing on a buss that was also supplying load to branch circuits and feeders.
Anyhow I think we all have come to an agreement there are code issues that need to be addressed with what the OP posted and the concerns the OP had with that installation involving a main lug panel for the service disconnect.
