200 amp meter main breaker located at the center of the panel.

[ACABE]

I installed a 200 amp panel Murray surface mount with meter on left and breakers on the right with the main breaker located at the center of the panel by manufacture. My customer call me today and tells me that the panel I installed is not up to new code when installing a solar panels. The solar company told me that Los Angeles County in CA does not allow the Main Breaker to be position in the center of the panel because of the 125% RULE either at top or bottom. Does anyone had this situation?

 

[don_resqcapt19]

I installed a 200 amp panel Murray surface mount with meter on left and breakers on the right with the main breaker located at the center of the panel by manufacture. My customer call me today and tells me that the panel I installed is not up to new code when installing a solar panels. The solar company told me that Los Angeles County in CA does not allow the Main Breaker to be position in the center of the panel because of the 125% RULE either at top or bottom. Does anyone had this situation?

The rule in 705.12(D)(7) says the solar breaker has to be at the "opposite end" of the bus from the main breaker. Many AHJs read that prohibiting the installation of a solar production breaker in a panel with a center main.

 

[ggunn]

I installed a 200 amp panel Murray surface mount with meter on left and breakers on the right with the main breaker located at the center of the panel by manufacture. My customer call me today and tells me that the panel I installed is not up to new code when installing a solar panels. The solar company told me that Los Angeles County in CA does not allow the Main Breaker to be position in the center of the panel because of the 125% RULE either at top or bottom. Does anyone had this situation?

Yeah, those panels have been the subject of many spirited discussions on solar forums, with no clear resolution. The NEC does not address the issue directly. Logically, as long as the busbars have a rating equal to or more than than the rating of the main breaker, it seems to me that either end (or both ends) is/are the "opposite" end(s) from the main breaker. Think of it as two smaller panels fed by the same main. Some AHJ's apparently do not see it this way. Luckily for me, so far I have not had to deal with a panel of this type.

EDIT: Upon further review, I can also come up with a contrary way of thinking of it. Say the inverter is running flat out and all the loads on the same end of the busbar are off, and the panel has a lot of active loads on the other end of the busbar from the inverter breaker. The current available to them is the rating of the main plus the rating of the backfed breaker and all of it passes through the part of the busbar on their side of the main. That's the situation that the rule that the main and inverter breakers have to be on opposite ends of the bar is written to prevent. Never mind what I said before...

 

[jaggedben]

It should be mentioned that this is only an issue if the main breaker is the same rating as the busbar. In a panel with a 225A busbar and 200A main breaker (for example) you could install 25A of solar wherever you like.

There is really no danger involved if the load breakers on the end opposite the solar do not exceed the rating of the busbar. For this reason, I almost always try to install the solar breaker on the 'longer end' of the panel, just to make it less likely for the load breakers at the other end to end up being too much. But this is neither foolproof nor an argument that you can use with an AHJ.

The 2014 code will allow interconnecting in center fed panels under 'engineering supervision'. But we're three years away from that in CA.

 

[ggunn]

It should be mentioned that this is only an issue if the main breaker is the same rating as the busbar. In a panel with a 225A busbar and 200A main breaker (for example) you could install 25A of solar wherever you like.

There is really no danger involved if the load breakers on the end opposite the solar do not exceed the rating of the busbar. For this reason, I almost always try to install the solar breaker on the 'longer end' of the panel, just to make it less likely for the load breakers at the other end to end up being too much. But this is neither foolproof nor an argument that you can use with an AHJ.

The 2014 code will allow interconnecting in center fed panels under 'engineering supervision'. But we're three years away from that in CA.

Would you be able to install 2 20A inverter breakers in a 200A (Main breaker and busbar) center fed panel if they were placed at opposite ends from each other with the main breaker between them?

 

[GoldDigger]

Would you be able to install 2 20A inverter breakers in a 200A (Main breaker and busbar) center fed panel if they were placed at opposite ends from each other with the main breaker between them?

No.

 

[jaggedben]

Would you be able to install 2 20A inverter breakers in a 200A (Main breaker and busbar) center fed panel if they were placed at opposite ends from each other with the main breaker between them?

If the loads on neither side of the main exceed 200A then I don't see a danger. But I'm not an engineer. And I don't think the code allows it.

 

[ggunn]

If the loads on neither side of the main exceed 200A then I don't see a danger. But I'm not an engineer. And I don't think the code allows it.

When I thought about it for a minute I realized that the scenario was not fundamentally different from the one I proposed earlier which was a potential problem. The only difference is that the potential "hot spot" on the busbars would be at 110% of the rating instead of 120%.

As to the total loads, it is always the case that the sum of the ratings of the load breakers can exceed the rating of the main breaker and busbars. The assumption is that the probability of all the load breakers maxxing out is very low, but if it happens the main breaker will trip. Once you add PV to the equation, however, you add the available current from the PV to that from the main breaker, hence the 120% and breaker placement rules.

 

[GoldDigger]

When I thought about it for a minute I realized that the scenario was not fundamentally different from the one I proposed earlier which was a potential problem. The only difference is that the potential "hot spot" on the busbars would be at 110% of the rating instead of 120%.

As to the total loads, it is always the case that the sum of the ratings of the load breakers can exceed the rating of the main breaker and busbars. The assumption is that the probability of all the load breakers maxxing out is very low, but if it happens the main breaker will trip. Once you add PV to the equation, however, you add the available current from the PV to that from the main breaker, hence the 120% and breaker placement rules.

The interesting thing about that observation is that as long as the PV and main breakers are on opposite sides of the load breakers along the bud, no single point in the bus will in fact carry any more current than the larger if the two (PV and main).

So the 120% rule is not needed when the opposite end rule is satisfied and is not enough to insure safety when the opposite end rule is violated.

If you put loads rated at more than the bus on the opposite side of the central main from the PV, then you can overload the bus even if the 120% (or 110%) rule is
observed.

 

[ggunn]

The interesting thing about that observation is that as long as the PV and main breakers are on opposite sides of the load breakers along the bud, no single point in the bus will in fact carry any more current than the larger if the two (PV and main).

So the 120% rule is not needed when the opposite end rule is satisfied and is not enough to insure safety when the opposite end rule is violated.

I have contemplated such things and come to pretty much the same conclusions, but "interesting" is subjective. It's interesting to me, but if I were to say such a thing to my wife, I would get the eyeroll.

If you put loads rated at more than the bus on the opposite side of the central main from the PV, then you can overload the bus even if the 120% (or 110%) rule is
observed.

If you deconvolute the tortured first sentence of 705.12(D)(7), I'm pretty sure that's what it is trying to say.