2020 705.12(B)(3)(3)

[TallTimber]

Hello all, I know this has been discussed on several occasions but I cannot seem to lock down a solid answer on way or the other. I have a project I am working on where a customer is attempting to back feed solar through an 80A breaker on a 200A MSP with a 200A MSB. The customer has (4) 20A breakers on this panel. This panel also feeds a 200A sub panel via the feed through lugs. The customer is stating that 705.12(B)(3)(3) sum method allows this since the code states:

"(3) The sum of the ampere ratings of all overcurrent devices on panelboards, both load and supply devices, excluding the rating of the overcurrent device protecting the busbar, shall not exceed the ampacity of the busbar. The rating of the overcurrent device protecting the busbar shall not exceed the rating of the busbar. Permanent warning labels shall be applied to distribution equipment displaying the following or equivalent wording:"

The customers argument is in the wording "on panelboards". They interpret the code that since the sub panel 200A breaker is not physically ON the 200A MSP bus bar then it does not count.

It is my interpretation that "all overcurrent devices on panelboards" includes all devices on any board between the MSB and first OCD. It could also be argued that while the device may not be physically on the panelboard it is on the same node as the other OCD's and is thus electrically on the panelboard. It seems to me that if the NEC wanted only breakers on the panel then it should be written "all overcurrent devices on the panelboard on panelboards"

If we allowed a subpanel on a feed through to not be counted towards an upstream bus, then would be an allowable possibility that a customer could chain an unlimited amount of sub panels and back feed any solar quantity they want.

I am not a fan of trying to create loop holes that are inherently unsafe.

 

[jaggedben]

"Loophole" is an appropriate term for the feed through lugs situation.

See 705.12(B)(3)(6) for the 2020 language about feed through lugs. It was slightly changed in the 2023 to allow the 200A sub breaker to permit the MSP to use the normal rules. Both codes say that if you have this OCPD, then you can size the MSP bus to 705.12(B)(3)(3) or other rules. (Which sort of implies that if you don't have it, you can't.) What the code doesn't quite come out and say is that the sub's 200A main breaker should count toward the sum.