Connection of Multiple Solar Circuits

[Auburn1]

I am seeing some solar installations with multiple solar circuits at the main panel. Is it possible to utilize the 120% rule (where the solar breaker is required to be at the opposite end of the busbar) when multiple solar circuits are landed on the bus? Example: Existing 200A panel with existing 20A solar breaker at farthest end of busbar. New installer upgrades the system and adds an additional 20A solar breaker opposite the existing 20A solar breaker. Can both solar breakers be considered at the opposite end of the busbar? Since the breakers are slightly staggered can they both be considered opposite end or do they need to be combined in a combiner box and landed at a single 40 solar breaker?

 

[GoldDigger]

I am seeing some solar installations with multiple solar circuits at the main panel. Is it possible to utilize the 120% rule (where the solar breaker is required to be at the opposite end of the busbar) when multiple solar circuits are landed on the bus? Example: Existing 200A panel with existing 20A solar breaker at farthest end of busbar. New installer upgrades the system and adds an additional 20A solar breaker opposite the existing 20A solar breaker. Can both solar breakers be considered at the opposite end of the busbar? Since the breakers are slightly staggered can they both be considered opposite end or do they need to be combined in a combiner box and landed at a single 40 solar breaker?

For practical purposes, there is no chance of a load breaker (or feed through) being on the same side of both the main and the backfed breaker(s), so it meets the intent of the 120% rule should be OK. There is no way that any part of the bus will be carrying the sum of the two (or more) currents. From a regulatory viewpoint, however, it may depend on your AHJ.

Interesting. I had not thought before of the fact that, whether or not the language of the section covers it explicitly, the purpose of the rule cannot be met if there are feed-through lugs to a second panel in the panelboard where the backfeed is located, at the opposite end of the bus from the main. Possibly not even allowed by the AHJ if there are feed through lugs but they are not used!

 

[jaggedben]

I am seeing some solar installations with multiple solar circuits at the main panel. Is it possible to utilize the 120% rule (where the solar breaker is required to be at the opposite end of the busbar) when multiple solar circuits are landed on the bus? Example: Existing 200A panel with existing 20A solar breaker at farthest end of busbar. New installer upgrades the system and adds an additional 20A solar breaker opposite the existing 20A solar breaker. Can both solar breakers be considered at the opposite end of the busbar? Since the breakers are slightly staggered can they both be considered opposite end or do they need to be combined in a combiner box and landed at a single 40 solar breaker?

I've always regarded the last busbar stabs as the opposite end, and never been challenged on this. There is no electrical sense in which any load or source circuit connected to those stabs is more or less 'opposite end' than any other. Most of the time that means that more than circuit can be there. If it is an Eaton or Siemens panel or one of their similar predecessors, then a 'quad' breaker with (2) two-pole circuits can go on those stabs. And if it is a 'two-column' construction, you could have up to four circuits that are all 'opposite end' on those two stabs. With Homeline or GE you don't get those type of quads, but you could still have two opposite end circuits with a two-sided construction. With a single-column (typical of side-by-side meter main combos), you'd typically be limited to half the number you'd get with two-column construction.

An argument could be made that one could put in as many circuits as otherwise possible, as long as they started at the opposite end and filled up all the spaces towards that end, and all had the 'do not relocate' label on them.

I don't know what you mean by the breaker being 'slightly staggered'. Either one is not really at the opposite end, but probably could be, or else I think you are misunderstanding the panelboard construction.

...

A somewhat different but related example: I recently had a system that had a single-phase inverter backfeeding only the 'split-phase' portion of a high-leg delta. That is, the inverter connected to the A and C phase and not to the 'B' high leg. The breaker needed to go opposite end in the panel, and of course the order of the stabs at the bottom was A,B,C. At one point I momentarily freaked out that I could not put a two-pole breaker across the A and C legs, because in order to do so I would have to use the C stab that was three positions up from the bottom, instead of the very bottom stab that was 'opposite end'. Solution: Use a three pole breaker and just don't hook up anything to the B leg. That breaker was able to use the bottom most A and C stabs.