Is it legal to land multiple solar backed breakers in one panel?

JoeNorm

Senior Member
Location
WA
Ive never done this before, we have always combined circuits and then landed one breaker in the correct location on the bus bar.

But it got me wondering, if there is a main panel with the space and proper rating, could you land multiple backed breakers?

Code references welcome

Thanks
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Yes. I've done it many many times.
But it's kind of a gray area if there are more than two and you are qualifying the bus under the 120% rule, since if there are three, one of them cannot be at the opposite end of the bus from the utility feed. There's no problem electrically but the inspecting AHJ might flag it.
 

JoeNorm

Senior Member
Location
WA
From a busbar protection standpoint I'd say spreading the input over multiple breakers would be better, right? As opposed to delivering it at one point. I know you're saying it could be a technicality thing, but I never liked technicalities that were not backed by basic logic.
 

jaggedben

Senior Member
But it's kind of a gray area if there are more than two and you are qualifying the bus under the 120% rule, since if there are three, one of them cannot be at the opposite end of the bus from the utility feed. There's no problem electrically but the inspecting AHJ might flag it.
If you happen to have a side-by-side arrangement in a single-phase panel that allows double 2-pole quad breakers in two spaces (Eaton BR and Murray/Siemens being the only ones I know of), then you can put four 2-pole circuits at the opposite end of the busbar. If it is none of those things your statement is true, and for some panels it would be true with only one breaker.

As for grey areas, here's a thought experiment. Let's say I have a 200A panel fed by a 175A breaker and I want to put 3 20A micro-inverter circuits in it. Two of them are using the 120% and must fit at the opposite end. Can I put the third one wherever I please? :cool:
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
As for grey areas, here's a thought experiment. Let's say I have a 200A panel fed by a 175A breaker and I want to put 3 20A micro-inverter circuits in it. Two of them are using the 120% and must fit at the opposite end. Can I put the third one wherever I please? :cool:
It seems to me that logically, yes, because even loads between your third breaker and the two at the end of the busbar could only draw 235A, which is still less than 120% of the busbar rating. Good luck convincing an AHJ that it is code compliant, though. :D
 

pv_n00b

Senior Member
Location
CA, USA
NEC 705.12 does not limit the number of PV system interconnections into a panel. But I have run across some utilities that only allow a single PV disconnect for all systems. When adding to an existing PV system I have had to rewire the existing system and the new system together so they have a single disconnect. A real pain if the inverter AC voltages are not the same. I have not run into an AHJ that has called out multiple PV CBs at the end of the panel as being a problem. I guess anything is possible but as long as a load can't be added after the PV CBs it should be good.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
NEC 705.12 does not limit the number of PV system interconnections into a panel. But I have run across some utilities that only allow a single PV disconnect for all systems. When adding to an existing PV system I have had to rewire the existing system and the new system together so they have a single disconnect. A real pain if the inverter AC voltages are not the same.
When would they be different? I don't see how that would make things harder; if the AC voltages were different at least one of them would not match the service voltage and you'd have to have a transformer in either case.
 

jaggedben

Senior Member
When would they be different? I don't see how that would make things harder; if the AC voltages were different at least one of them would not match the service voltage and you'd have to have a transformer in either case.
Well you might have a premise that already has a service voltage and an SDS voltage, and you might have an existing system tied into one and a new system sold with inverters that match the other, and be forced to add a new transformer.
 

Carultch

Senior Member
Location
Massachusetts
NEC 705.12 does not limit the number of PV system interconnections into a panel. But I have run across some utilities that only allow a single PV disconnect for all systems. When adding to an existing PV system I have had to rewire the existing system and the new system together so they have a single disconnect. A real pain if the inverter AC voltages are not the same. I have not run into an AHJ that has called out multiple PV CBs at the end of the panel as being a problem. I guess anything is possible but as long as a load can't be added after the PV CBs it should be good.
One way to work within that rule, is to use 4-pole (single phase) and 6-pole (3-phase) disconnects, so the utility's required switch can have the same throw of the hand, shut off both systems at once.
 

pv_n00b

Senior Member
Location
CA, USA
When would they be different? I don't see how that would make things harder; if the AC voltages were different at least one of them would not match the service voltage and you'd have to have a transformer in either case.
The last one I looked at had the existing PV system interconnecting behind a customer owned 480-208V transformer and the new PV system would interconnect at 480V. A new 208-480V transformer was needed to get the existing system up to the service voltage and combine it with the new PV system. The interconnection point for the old system did not have the capacity for both anyway.

One way to work within that rule, is to use 4-pole (single phase) and 6-pole (3-phase) disconnects, so the utility's required switch can have the same throw of the hand, shut off both systems at once.
I had not thought of doing that, an interesting solution.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
(I understand solar basics, but haven't installed a system, so please be kind.)

It seems logical to me that a system that needs several solar-power breakers should have a sub-panel for those, and a single inter-tie between the solar panel and the main power panel.

So, where's the flaw in that idea?
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
(I understand solar basics, but haven't installed a system, so please be kind.)

It seems logical to me that a system that needs several solar-power breakers should have a sub-panel for those, and a single inter-tie between the solar panel and the main power panel.

So, where's the flaw in that idea?
No flaw, and that's what we usually do. In some jurisdictions we have to, like any that require a single PV meter.
 

jaggedben

Senior Member
(I understand solar basics, but haven't installed a system, so please be kind.)

It seems logical to me that a system that needs several solar-power breakers should have a sub-panel for those, and a single inter-tie between the solar panel and the main power panel.

So, where's the flaw in that idea?
It's not the systems that need several breakers where you end up asking about this. It's the system that needs two, or maybe three, and the existing panel has lots of space. It's nice to save money.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
It's not the systems that need several breakers where you end up asking about this. It's the system that needs two, or maybe three, and the existing panel has lots of space. It's nice to save money.
I understand, and agree that there is no one best design that covers every situation. My only thought was two separable systems.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
Are you using special listed breakers that don't require a hold down when backfed? Or are you using panels that allow these breaker clamps in every slot? The few panels I've looked at where you can put in a back fed breaker hold down typically has them at the corners of the panelboard (and maybe only 2 positions have the screw hole and not all 4).
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Are you using special listed breakers that don't require a hold down when backfed? Or are you using panels that allow these breaker clamps in every slot? The few panels I've looked at where you can put in a back fed breaker hold down typically has them at the corners of the panelboard (and maybe only 2 positions have the screw hole and not all 4).
PV inverters do not require tiedowns on their interconnection breakers.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Engineer
They don't? What about 705.12(B)(5). Fastening. Listed plug-in-type circuit breakers backfed from electric power sources that are listed and identified as interactive shall be permitted to omit the additional fastener normally required by 408.36(D) for such applications.

Maybe it is how you interpret the words... is the "that are listed and identified as interactive" modifying plug-in circuit breakers or electric power sources? Without any commas, you may be right that feeding a breaker from a listed and identified interactive power source is all you need to eliminate the hold down. I was reading it the other way (e.g. there could be plug-in circuit breaker that are listed as "interactive" types and only those don't need the hold down).
 

Carultch

Senior Member
Location
Massachusetts
They don't? What about 705.12(B)(5). Fastening. Listed plug-in-type circuit breakers backfed from electric power sources that are listed and identified as interactive shall be permitted to omit the additional fastener normally required by 408.36(D) for such applications.

Maybe it is how you interpret the words... is the "that are listed and identified as interactive" modifying plug-in circuit breakers or electric power sources? Without any commas, you may be right that feeding a breaker from a listed and identified interactive power source is all you need to eliminate the hold down. I was reading it the other way (e.g. there could be plug-in circuit breaker that are listed as "interactive" types and only those don't need the hold down).
The intent of requiring a fastener for backfed plug-on breakers, is for power sources that remain energized after the breaker is set to the off-position, or unplugged from the busbars. Examples of where this would apply are generators, utility services, and feeders from an upstream panel to the subpanel in question. Essentially using a branch breaker as the main breaker of the panel. The idea is to make an extra step in unplugging the breaker from the busbar, due to its wires still being energized.

Inverters are an exception, because by contrast, they will automatically de-energize the AC-side, if the voltage is no longer within the tolerance. Remove the voltage, and it ceases to be able to apply current to the line. Inverters first look for a voltage within tolerance, and then after a UL-required 5 minute delay, will begin backfeeding current to the line. Unlike other sources that generate their own voltage first, and allow current to follow when the load is connected.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
They don't? What about 705.12(B)(5). Fastening. Listed plug-in-type circuit breakers backfed from electric power sources that are listed and identified as interactive shall be permitted to omit the additional fastener normally required by 408.36(D) for such applications.
No, they don't, and the verbage you quote is the enabling language. Carltuch explained it well; I have nothing to add.
 
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