Understanding Better 705.12 Case

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Baker Makarem

Member
Location
FL
Occupation
Solar
Hey Everyone. I have this case about a PV interconnection load side to a Metermain combo which also has feedthrough lugs to a subpanel inside the house. Do we need to comply with 705.12.B.2 through 1 to 3. ? this include feeder part, Tap and Busbar. I am not sure if go all the way literally with what it said on NEC2017: 705.12.B " ....shall comply with 705.12.B.1 through B.5"

see attached picture of what I am trying to do.

Line diagram IMAGE
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Hey Everyone. I have this case about a PV interconnection load side to a Metermain combo which also has feedthrough lugs to a subpanel inside the house. Do we need to comply with 705.12.B.2 through 1 to 3. ? this include feeder part, Tap and Busbar. I am not sure if go all the way literally with what it said on NEC2017: 705.12.B " ....shall comply with 705.12.B.1 through B.5"

see attached picture of what I am trying to do.

Line diagram IMAGE
705.12(B) does not apply to the sub panel because it is protected by a main breaker and it is not in the current path between the inverter and the service.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
The interconnection at the feeder from the subfeed lugs to the subpanel needs to comply with the feeder rules in 705.12, which it appears to, as the subpanel has a main breaker.

The meter main will need to comply with the busbar rules in 705.12, and it appears to comply with the 120% rule, since the inverter is fused at 40A and the meter main has a 200A main breaker.

The feeder tap from the 200A feeder to the 40A PV fuses is protected at 200A from the utility side, so it needs a 200A ampacity, or to comply with the feeder tap rules in 240.21(B).

Cheers, Wayne
 

Baker Makarem

Member
Location
FL
Occupation
Solar
thank you Guys, I now understand better, Once I place a Main Breaker at the Sub panel, this will no longer be an extension of the Busbar in the Main panel, it will be considered a branch circuit.
 

Carultch

Senior Member
Location
Massachusetts
thank you Guys, I now understand better, Once I place a Main Breaker at the Sub panel, this will no longer be an extension of the Busbar in the Main panel, it will be considered a branch circuit.
That's correct. The main breaker in the subpanel, doesn't care what mixture of sources supply its line side. Given that it is the only source supplying the panel, it protects its busbar against overload, no matter what could supply over 200A to its loads.

The 705.12(B) rules regarding busbars are concerned with feeding the busbar with a source, that is in the blindspot of the main breaker, which is what you do when you backfeed one of its load breakers, or anything on the load side of a panel's main. Panels are routinely filled with more breakers than their main breaker's rating, and if the busbar is depending on the main to prevent overload, a second source within the panel could put that overload in its blindspot.
 
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