Rejection - Need Help (Please)

[Npstewart]

Hello.

I've been posting on this forum for around 15 years and been in the industry for longer. However, Solar / PV systems simply is not my specialty and out of all the codes I know in the NEC - The PV/Solar one is not one of them - so im looking for some help.

I own a home in Florida so I hired a company to install solar panels. However, the company hired an Engineer, and the Engineer is on his 3rd rejection with the City. His rejections are a bit ambiguous so im looking for someone to see if these rejections are valid.

Im posting the rejections, in addition to the latest set of drawings that were submitted.

ANY help would be appreciated. Please note that im attaching the drawings but I extracted just the riser / panel schedule pages.

Drawings Attached:




REMAINING REVIEW COMMENTS (3RD SUBMITTAL):

COMMENT #1
2017 NEC: 1- Please provide a panel schedule for both the MSP and MDP to substantiate the requirements of 705.12(B)(2)(3)(c). 2- Please provide the bus rating of the MSP. 3- Please provide the MCB rating of the MSP. 4- The label sheets needs to include the required labeling per Article 705.



COMMENT #2
705.12(B)(3)(c) requires that the sum of all OCPD's supplying and/or being supplied by are factored for. The ATS which supplies the MDP is being supplied by the feeders terminated on the feed through lugs that are connected to the MSP's busbar. Please provide a panel schedule for the MDP and factor for those OCPD's.



COMMENT #3
705.12(B)(3)(6) of the 2020 NEC clarifies the interconnection rules for busbars. You are permitted backfeed a circuit breaker at the feed through panel, but there needs to be an OCPD at the supply end of the feed through conductors that is rated no larger than the rating of the feed through conductors. For example, if you were to add 175A breaker on the subpanel that is being fed from the feed through conductors you would be compliant. Code Language-Connections shall be permitted on busbars of panelboards that supply lugs connected to feed-through conductors. The feed-through conductors shall be sized in accordance with 705.12(B)(1). Where an overcurrent device is installed at the supply end of the feed-through conductors, the busbar in the supplying panelboard shall be permitted to be sized in accordance with 705.12(B)⁠(3)⁠(1) through 705.12(B)(3)(3)

 

[wwhitney]

The drawing shows a 200A meter/main/distribution with a 20A load, at the bottom a 50A breaker for 35A of continuous PV inverter output (29 microinverters @ 1.21A), and below that feed thru lugs to a generator automatic transfer switch with a 200A OCPD which supplies a panel with all the other loads. The drawing references (2020) 705.12(B)(3)(3) for the service panelboard.

Interconnection in panels with feed-thru lugs is definitely a grey area, so it's not surprising there have been multiple rejections. Personally, I don't agree with the part of Comment #3 that says "For example, if you were to add 175A breaker on the subpanel that is being fed from the feed through conductors you would be compliant," but how to apply 705.12(B)(3)(6) is not crystal clear.

So if you're happy replacing the 200A OCPD in the ATS with a 175A OCPD, that is a simple way forward. While I don't feel that complies with 705.12(B)(3)(3) and (6), there's still no chance of the configuration shown overloading the service panel bus. [The rules in 705.12(B)(3) are a compromise for simplicity, rather than attempting to exhaustively allow any reasonable configurations.]

What I would consider compliant would be to either (a) lose 3 panels/microinverters, so that you can use a 40A breaker for the PV interconnection or (b) change the service panel main OCPD to 175A. Either way that complies with 705.12(B)(3)(2) and (6). There are also more complicated configurations that wouldn't require either of those compromises.

Cheers, Wayne

 

[Npstewart]

The drawing shows a 200A meter/main/distribution with a 20A load, at the bottom a 50A breaker for 35A of continuous PV inverter output (29 microinverters @ 1.21A), and below that feed thru lugs to a generator automatic transfer switch with a 200A OCPD which supplies a panel with all the other loads. The drawing references (2020) 705.12(B)(3)(3) for the service panelboard.

Interconnection in panels with feed-thru lugs is definitely a grey area, so it's not surprising there have been multiple rejections. Personally, I don't agree with the part of Comment #3 that says "For example, if you were to add 175A breaker on the subpanel that is being fed from the feed through conductors you would be compliant," but how to apply 705.12(B)(3)(6) is not crystal clear.

So if you're happy replacing the 200A OCPD in the ATS with a 175A OCPD, that is a simple way forward. While I don't feel that complies with 705.12(B)(3)(3) and (6), there's still no chance of the configuration shown overloading the service panel bus. [The rules in 705.12(B)(3) are a compromise for simplicity, rather than attempting to exhaustively allow any reasonable configurations.]

What I would consider compliant would be to either (a) lose 3 panels/microinverters, so that you can use a 40A breaker for the PV interconnection or (b) change the service panel main OCPD to 175A. Either way that complies with 705.12(B)(3)(2) and (6). There are also more complicated configurations that wouldn't require either of those compromises.

Cheers, Wayne

Thanks so much Wayne.

I’d be pretty upset if I had to replace the 200A breaker in the ATS. I put the ATS in myself and it’s a 200A SER switch. I’m not even sure if Generac manufacturers anything other than a 200A breaker for this SER switches.

What puzzles me is the fact that my Electric service and setup is pretty much a boiler-plate electric service and an 11.3kW system is probably one of the most common sizes for solar systems in Florida, because this is the max system size you can have without buying liability insurance in this state .

So, in my mind I have a boiler -plate setup across the board for an extended service, but for some reason it’s extremely difficult at the same time.

I just can’t imagine so many people have this identical issue.

 

[Npstewart]

Also, not sure if it matters but the reviewer referenced the 2020 NEC. However, Florida is still on the 2017 NEC.

 

[ggunn]

Hello.

I've been posting on this forum for around 15 years and been in the industry for longer. However, Solar / PV systems simply is not my specialty and out of all the codes I know in the NEC - The PV/Solar one is not one of them - so im looking for some help.

I own a home in Florida so I hired a company to install solar panels. However, the company hired an Engineer, and the Engineer is on his 3rd rejection with the City. His rejections are a bit ambiguous so im looking for someone to see if these rejections are valid.

Im posting the rejections, in addition to the latest set of drawings that were submitted.

ANY help would be appreciated. Please note that im attaching the drawings but I extracted just the riser / panel schedule pages.

Drawings Attached:




REMAINING REVIEW COMMENTS (3RD SUBMITTAL):

COMMENT #1
2017 NEC: 1- Please provide a panel schedule for both the MSP and MDP to substantiate the requirements of 705.12(B)(2)(3)(c). 2- Please provide the bus rating of the MSP. 3- Please provide the MCB rating of the MSP. 4- The label sheets needs to include the required labeling per Article 705.



COMMENT #2
705.12(B)(3)(c) requires that the sum of all OCPD's supplying and/or being supplied by are factored for. The ATS which supplies the MDP is being supplied by the feeders terminated on the feed through lugs that are connected to the MSP's busbar. Please provide a panel schedule for the MDP and factor for those OCPD's.



COMMENT #3
705.12(B)(3)(6) of the 2020 NEC clarifies the interconnection rules for busbars. You are permitted backfeed a circuit breaker at the feed through panel, but there needs to be an OCPD at the supply end of the feed through conductors that is rated no larger than the rating of the feed through conductors. For example, if you were to add 175A breaker on the subpanel that is being fed from the feed through conductors you would be compliant. Code Language-Connections shall be permitted on busbars of panelboards that supply lugs connected to feed-through conductors. The feed-through conductors shall be sized in accordance with 705.12(B)(1). Where an overcurrent device is installed at the supply end of the feed-through conductors, the busbar in the supplying panelboard shall be permitted to be sized in accordance with 705.12(B)⁠(3)⁠(1) through 705.12(B)(3)(3)

I don't think you can use 705.12(B)(2)(3)(c) to qualify the bus in the meter main because the 200A breaker in the ATS counts as a device connected to the bus. The sum of the connected devices is 270A.

 

[jaggedben]

He shouldn't be asking for a panel schedule for the MDP. Everything after the OCPD in the ATS is irrelevant to the interconnection. But I agree with everything the others said about making it code compliant.

Downsizing the service main breaker to 175A is probably the way to go. Do you really need more than 42kW?

 

[Npstewart]

I just spoke with the plans examiner because I doubt the engineer designing the system even tried to call.

When I installed the generator, I used 3/0 Cu conductors. According to him, because the 3/0s are rated for 200A, everything is OK and that just needs to be adjusted on the riser.

Im not sure if that is correct because 3 feet of wiring is cheaper and faster to reinstall vs. finding a 175A breaker these days and would have thought he would have suggested that.

 

[Npstewart]

He shouldn't be asking for a panel schedule for the MDP. Everything after the OCPD in the ATS is irrelevant to the interconnection. But I agree with everything the others said about making it code compliant.

Downsizing the service main breaker to 175A is probably the way to go. Do you really need more than 42kW?

Thanks.

No, I dont but I have (1) EV and if I put in another then I might. I monitor my power usage with a monintor and I dont think i've ever seen it go about 17kW sustained usage, and the most its ever peaked is about 22kW.

 

[solarken]

COMMENT #2
705.12(B)(3)(c) requires that the sum of all OCPD's supplying and/or being supplied by are factored for. The ATS which supplies the MDP is being supplied by the feeders terminated on the feed through lugs that are connected to the MSP's busbar. Please provide a panel schedule for the MDP and factor for those OCPD's.



COMMENT #3
705.12(B)(3)(6) of the 2020 NEC clarifies the interconnection rules for busbars. You are permitted backfeed a circuit breaker at the feed through panel, but there needs to be an OCPD at the supply end of the feed through conductors that is rated no larger than the rating of the feed through conductors. For example, if you were to add 175A breaker on the subpanel that is being fed from the feed through conductors you would be compliant. Code Language-Connections shall be permitted on busbars of panelboards that supply lugs connected to feed-through conductors. The feed-through conductors shall be sized in accordance with 705.12(B)(1). Where an overcurrent device is installed at the supply end of the feed-through conductors, the busbar in the supplying panelboard shall be permitted to be sized in accordance with 705.12(B)⁠(3)⁠(1) through 705.12(B)(3)(3)

If you install the Enphase Enpower controller/ATS, you can land both the generator and the PV combiner output in the ATS, and eliminate all these issues, and have a more integrated, seamless result. You can install up to 80A of PV, and also accomodate battery storage easily in the future. The way you have it now, with the main service disconnect being the 200A breaker in the Meter/Main, I see a load-side connection in the M/M that violates the 120% rule. If you are able to downsize the main breaker in the M/M to 175A that would give you budget needed for the 50A backfed breaker.

 

[wwhitney]

Also, not sure if it matters but the reviewer referenced the 2020 NEC. However, Florida is still on the 2017 NEC.

FYI, the 2017 NEC is silent on how to handle feed-thru lugs in 705.12(B). So you are going to find a lot of variation in how AHJs apply the 2017 NEC to this sort of situation. Looking to future versions of the NEC that do address feed-thru lugs is a reasonable approach in this situation.

Anyway, do I understand correctly that your plans examiner just wants the plans updated to specify the existing 3/0 Cu, and doesn't want any other changes? If so, you're good to go, and while that's plausible given the silence of the 2017 NEC on the matter of feed thru lugs, I don't agree it complies with the intention of the later NECs.

But as I initially said, there's no bus overload issue with your configuration, simply because you have so few load breakers in the service panel, so the only reason later NECs would prohibit this configuration is the apparent impossibility of writing simple but all-encompassing rules.

Cheers, Wayne

 

[Zee]

Didn't read all the details, sorry!
One point: never had an issue in 20 years after installing a 175A breaker to replace the 200A main breaker.

 

[topgone]

I may be late but the questionable thing in the interconnection design is that the PV breaker exceeds what the 120% rule says.
The interconnection of the 200A service with a 200A protection device needs to have a 1.2 X 200 -200 = 40A for the PV. 50A is installed for the PV feed. By that, the code stipulation is violated by 10A.
PV breaker+Main OCPD must be lesser than or equal to 120% of busbar rating -->50 +200 = 250 is not lesser than or equal to 1.2 X 200=240!

 

[Carultch]

I may be late but the questionable thing in the interconnection design is that the PV breaker exceeds what the 120% rule says.
The interconnection of the 200A service with a 200A protection device needs to have a 1.2 X 200 -200 = 40A for the PV. 50A is installed for the PV feed. By that, the code stipulation is violated by 10A.
PV breaker+Main OCPD must be lesser than or equal to 120% of busbar rating -->50 +200 = 250 is not lesser than or equal to 1.2 X 200=240!

As of NEC2014, it is no longer the PV breaker that governs this calculation, but rather, 125% the total inverter current. If you start with a 50A breaker as a misguided solar-ready provision for PV on a 200A service panel (main & busbar), it doesn't matter that the breaker is 50A; all that matters is that 125% of the total inverter current is 40A or less.

 

[topgone]

As of NEC2014, it is no longer the PV breaker that governs this calculation, but rather, 125% the total inverter current. If you start with a 50A breaker as a misguided solar-ready provision for PV on a 200A service panel (main & busbar), it doesn't matter that the breaker is 50A; all that matters is that 125% of the total inverter current is 40A or less.

Precisely. The verbiage is:

Where two sources, one a primary power source and the other another power source, are located at opposite ends of a busbar that contains loads, the sum of 125 percent of the power-source(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed 120 percent of the ampacity of the busbar. The busbar shall be sized for the loads connected in accordance with Article 220 . . .

"125 percent of the power source(s)" means the breaker size from that power source feed! If we follow your logic, 40A *1.25 = 50A. Then, you add the OCPD rating of the said busbar (200A), and you get 250A. That is not equal to or lesser than 120% of the busbar rating (200A).

 

[wwhitney]

"125 percent of the power source(s)" means the breaker size from that power source feed!

No. If you have an inverter, with say a maximum continuous output current of 30A, then it means 125% * 30A = 37.5A. And not 40A, which is the smallest breaker you could use.

Cheers, Wayne

 

[Carultch]

Precisely. The verbiage is:

"125 percent of the power source(s)" means the breaker size from that power source feed! If we follow your logic, 40A *1.25 = 50A. Then, you add the OCPD rating of the said busbar (200A), and you get 250A. That is not equal to or lesser than 120% of the busbar rating (200A).

In my example, I'm saying the post-125% maximum amperes of the inverter output circuit, would be limited to 40A. The pre-125% value from the datasheet, would therefore be limited to 32A. The breaker rating you use to interconnect is now "out of the picture" of this rule, and instead, it's the theoretical minimum breaker you could use, prior to picking one from standard ratings, or using a larger-than-necessary breaker for other reasons.

An example where the 2014 change would swing a design:
Given a 600A busbar & a 600A main breaker of the main panelboard, 120% of 600A is 720A, so you have 120A of interconnection headroom available. Prior to 2014, 110A is the maximum standard breaker allowed in this example, which would govern 88A as the maximum total inverter output current. As of 2014, you'd be permitted to have up to 96A of inverter output current, which has a theoretical minimum breaker rating of 120A. 120A isn't a standard size, so you'd use a 125A breaker in practice. The 5A of "rounding error" is no longer a show stopper.