New main breaker in condo multimeter main service

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solarperson10

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Hello everyone,

At many duplexes, there is a multimeter main outside with just two main breakers. Those breakers feed each unit that has a MLO main distribution subpanel somewhere in the home, usually garage. When we install solar on duplexes, we land the inverter's breaker on the main distribution subpanel. The 120% rule is met because the breaker and and busbar rating math works out (EX: 200A MLO Main distribution subpanel in garage, 200A main breaker at MSP, with 40A of solar)

My company always takes an extra step of adding a main breaker to the main distribution subpanel. The new main breaker in the subpanel is the same capacity as the main breaker outside. Noone can tell me where the code says that the main breaker has to physically be attached to the bus bar to meet the 120% requirements. I would argue that we can leave the subpanel MLO and use the main breaker outside for the 120% rule.

No one I work with can give me evidence (NEC or CALIFORNIA ELECTRICAL CODE) for why we are adding the breaker. I have seen other companies design keeping the main distribution sub MLO.

Thanks
 
solarperson10 said:
Hello everyone,

At many duplexes, there is a multimeter main outside with just two main breakers. Those breakers feed each unit that has a MLO main distribution subpanel somewhere in the home, usually garage. When we install solar on duplexes, we land the inverter's breaker on the main distribution subpanel. The 120% rule is met because the breaker and and busbar rating math works out (EX: 200A MLO Main distribution subpanel in garage, 200A main breaker at MSP, with 40A of solar)

My company always takes an extra step of adding a main breaker to the main distribution subpanel. The new main breaker in the subpanel is the same capacity as the main breaker outside. Noone can tell me where the code says that the main breaker has to physically be attached to the bus bar to meet the 120% requirements. I would argue that we can leave the subpanel MLO and use the main breaker outside for the 120% rule.

No one I work with can give me evidence (NEC or CALIFORNIA ELECTRICAL CODE) for why we are adding the breaker. I have seen other companies design keeping the main distribution sub MLO.

Thanks
Click to expand...
https://imgur.com/Iei3oUF
 
solarperson10 said:
Noone can tell me where the code says that the main breaker has to physically be attached to the bus bar to meet the 120% requirements. I would argue that we can leave the subpanel MLO and use the main breaker outside for the 120% rule.
Click to expand...

I would agree as well. The 120% rule specifies the main overcurrent device protecting the busbar for this calculation, and doesn't specify the geography or mechanics of what this device is. It can be inside the panelboard as the main breaker, inside the panelboard as a branch breaker acting as a main, in an adjacent device, or in another room/location entirely. If you use an MLO panelboard and externalize the main to another device, then the rating of that externalized main OCPD takes the place of the main breaker in this calculation.

You might see this if there is a meter/main combo device outside feeding an MLO inside, or if you have an MLO subpanel supplied from the branch breaker. What ever OCPD is upstream of the panel in question, will act as its main breaker.

Where you WOULD need to introduce a new main OCPD where it might not exist initially, is if you are making the interconnection at a tap onto the feeder between the externalized main OCPD and the MLO panelboard. Doesn't necessarily need to be a breaker in the panel, as there are other options. It could also be a separate disconnect or ECB that intercepts the feeder. The tap point on the feeder would ultimately need to be "sandwiched" in between OCPDs that are capable of protecting both the feeder and downstream busbar.
 
Carultch said:
I would agree as well. The 120% rule specifies the main overcurrent device protecting the busbar for this calculation, and doesn't specify the geography or mechanics of what this device is. It can be inside the panelboard as the main breaker, inside the panelboard as a branch breaker acting as a main, in an adjacent device, or in another room/location entirely. If you use an MLO panelboard and externalize the main to another device, then the rating of that externalized main OCPD takes the place of the main breaker in this calculation.

You might see this if there is a meter/main combo device outside feeding an MLO inside, or if you have an MLO subpanel supplied from the branch breaker. What ever OCPD is upstream of the panel in question, will act as its main breaker.

Where you WOULD need to introduce a new main OCPD where it might not exist initially, is if you are making the interconnection at a tap onto the feeder between the externalized main OCPD and the MLO panelboard. Doesn't necessarily need to be a breaker in the panel, as there are other options. It could also be a separate disconnect or ECB that intercepts the feeder. The tap point on the feeder would ultimately need to be "sandwiched" in between OCPDs that are capable of protecting both the feeder and downstream busbar.
Click to expand...
While all this is true, one AHJ we have encountered will not allow a backfed breaker PV connection in a panel without a main breaker, and a disco ahead of an MLO panel doesn't satisfy them.
 
ggunn said:
While all this is true, one AHJ we have encountered will not allow a backfed breaker PV connection in a panel without a main breaker, and a disco ahead of an MLO panel doesn't satisfy them.
Click to expand...
The way I see it is we satisfy nec 225, 690, and 705. 225 says that the location of the busbar just has to be the same building. From what I understand the main breaker in the sub would only be necessary for a detached garage or shed structure. Thanks for the input!
 
Carultch said:
I would agree as well. The 120% rule specifies the main overcurrent device protecting the busbar for this calculation, and doesn't specify the geography or mechanics of what this device is. It can be inside the panelboard as the main breaker, inside the panelboard as a branch breaker acting as a main, in an adjacent device, or in another room/location entirely. If you use an MLO panelboard and externalize the main to another device, then the rating of that externalized main OCPD takes the place of the main breaker in this calculation.

You might see this if there is a meter/main combo device outside feeding an MLO inside, or if you have an MLO subpanel supplied from the branch breaker. What ever OCPD is upstream of the panel in question, will act as its main breaker.

Where you WOULD need to introduce a new main OCPD where it might not exist initially, is if you are making the interconnection at a tap onto the feeder between the externalized main OCPD and the MLO panelboard. Doesn't necessarily need to be a breaker in the panel, as there are other options. It could also be a separate disconnect or ECB that intercepts the feeder. The tap point on the feeder would ultimately need to be "sandwiched" in between OCPDs that are capable of protecting both the feeder and downstream busbar.
Click to expand...
Thanks for the input. I brought this forward to the largest AHJ we work in and their top inspector concurred. 120% rule is met, along with 225, no subpanel is needed as long as the the sub is in the same building as the main breaker/meter. Appreciate the response!
 
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