NEC 705.12(B)(3)(3) add loads and sources separately?

[ryangittens]

The way this code section reads sounds like they want the loads and the sources to be added together?

It would make more sense to me that if you add all the loads and you add all the soruces (excl. the main) separately and both add up to less than the bus bar rating the bus bar is still protected. For example a 200A panel with 200A worth of supply (excl. the main) and 200A worth of loads would be okay.

If we have a single 50A solar breaker connected to a 200A meter main combo with no other supply breakers and one 200A on the feedthrough conductors, is this compliant per this code section? If not, what code section applies here?

 

[wwhitney]

I believe the idea behind the rule is that you can quickly scan all the breakers (per leg) and confirm compliance. So it doesn't differentiate between loads and sources and just covers the case that every breaker could be either.

As to your last question, this section would not apply. Depending on the NEC year in force, you could argue that a panel with only 3 connections is exempt from 705.12(B), as it can not simultaneously have 2 sources of supply and itself supply multiple other pieces of equipment. But the relevant language that argument relies on is gone from the 2023 NEC.

The upshot is that the configuration doesn't comply with any of the prescriptive allowances. So you either need to use 2023 NEC 705.12(B)(6) engineering supervision, or you need to switch to a feeder interconnection. An obvious oversight in the rules of 705.12.

Cheers, Wayne

 

[jaggedben]

...
The upshot is that the configuration doesn't comply with any of the prescriptive allowances. So you either need to use 2023 NEC 705.12(B)(6) engineering supervision, or you need to switch to a feeder interconnection. An obvious oversight in the rules of 705.12.

Or if the inverter equipment is listed as a PCS you comply with 705.13 instead of 705.12.