Upstream breaker over subpanel breaker?

[hitehm]

We have a 150A main breaker panel that we need to install as a subpanel to land our solar breaker. Assume for now we can't find a lower amp main for the subpanel and the subpanel is on a separate building and requires a disconnect so it can't be MLO. The feeder breaker upstream in the main panel feeding this subpanel is 100A. So we will basically have a 100A main feeding a 150A main in the subpanel. Obviously, the 100A main breaker being upstream will limit the current to 100A. So as far as the 120% rule, can it be said that the breaker protecting the bus is 100A and the 150A breaker in the sub is acting solely as a disconnect and not as the bus OCPD?

 

[ggunn]

We have a 150A main breaker panel that we need to install as a subpanel to land our solar breaker. Assume for now we can't find a lower amp main for the subpanel and the subpanel is on a separate building and requires a disconnect so it can't be MLO. The feeder breaker upstream in the main panel feeding this subpanel is 100A. So we will basically have a 100A main feeding a 150A main in the subpanel. Obviously, the 100A main breaker being upstream will limit the current to 100A. So as far as the 120% rule, can it be said that the breaker protecting the bus is 100A and the 150A breaker in the sub is acting solely as a disconnect and not as the bus OCPD?

Yes. Electrically, the 150A main breaker is just a switch. You have 80A of electrical space in the panel.

 

[ggunn]

Yes. Electrically, the 150A main breaker is just a switch. You have 80A of electrical space in the panel.

And of course you have to apply 705.12(B)(3) in the main panel as well.

 

[hitehm]

And of course you have to apply 705.12(B)(3) in the main panel as well.

Thanks for the help sir. And I assume you mean because the inverter output is also back-feeding onto the main bus then the same rules apply.

The main panel happens to be one of those manufactured home pedestals. They are usually very old with no labels or they faded away long ago. See the pic, this one has a 100A and 200A main so we can hopefully assume the busbar is at least 300A.

 

[ggunn]

Thanks for the help sir. And I assume you mean because the inverter output is also back-feeding onto the main bus then the same rules apply.

The main panel happens to be one of those manufactured home pedestals. They are usually very old with no labels or they faded away long ago. See the pic, this one has a 100A and 200A main so we can hopefully assume the busbar is at least 300A.

View attachment 2565498

There isn't normally a busbar in those things.