Load Side Connection

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solarken

NABCEP PVIP
Location
Hudson, OH, USA
Occupation
Solar Design and Installation Professional
I have a site with 200A service into a Milbank 200A meter/main combo, with conductors from meter entering 200A main breaker at top of 200A busbar, lugs at the bottom of the busbar feeding a 200A house panel with 200A main breaker in it. Also on the meter main bus is a 100A breaker feeding an outbuilding, installed near top right of meter main. There are two open positions for a 240V backfed breaker for solar.
So considering the meter main:
200A can come down into bus from utility, limited by the main breaker
200A can exit the bus through the bottom lugs, limited by the house panel main breaker
100A can exit the bus to feed the outbuilding, limited by the breaker near top right of bus
48A x 1.25 = 60A can enter the bus, if I installed a 60A breaker at lower left position for the solar

No where on this bus is it possible to see more than 200A. Do you agree?

I believe, and ask for confirmation from you all, that 705.12(B)(2)(3)(c) of 2017NEC permits the above. The sum of the load and source breakers on the bus, 100A + 60A, excluding the 200A main that protects the bus is 160A which does not exceed the 200A busbar rating.

I also considered the following options:
A. Supply-side connection using Ilsco taps on the conductors between meter and main, but this would violate UL and not much room to do it.
B. Downsize main breaker from 200A to 175A with backfed breaker to keep within the 120% rule of 705.12(B)(2)(3)(b) of 2017 NEC. But this breaker cannot be found.
C. Load side connection by tapping the feeder to the house within the meter main enclosure.

I want to be prepared when I submit the permit and grid connection applications in case I get pushback so any advice would be appreciated.
 
solarken said:
I have a site with 200A service into a Milbank 200A meter/main combo, with conductors from meter entering 200A main breaker at top of 200A busbar, lugs at the bottom of the busbar feeding a 200A house panel with 200A main breaker in it. Also on the meter main bus is a 100A breaker feeding an outbuilding, installed near top right of meter main. There are two open positions for a 240V backfed breaker for solar.
So considering the meter main:
200A can come down into bus from utility, limited by the main breaker
200A can exit the bus through the bottom lugs, limited by the house panel main breaker
100A can exit the bus to feed the outbuilding, limited by the breaker near top right of bus
48A x 1.25 = 60A can enter the bus, if I installed a 60A breaker at lower left position for the solar

No where on this bus is it possible to see more than 200A. Do you agree?

I believe, and ask for confirmation from you all, that 705.12(B)(2)(3)(c) of 2017NEC permits the above. The sum of the load and source breakers on the bus, 100A + 60A, excluding the 200A main that protects the bus is 160A which does not exceed the 200A busbar rating.

I also considered the following options:
A. Supply-side connection using Ilsco taps on the conductors between meter and main, but this would violate UL and not much room to do it.
B. Downsize main breaker from 200A to 175A with backfed breaker to keep within the 120% rule of 705.12(B)(2)(3)(b) of 2017 NEC. But this breaker cannot be found.
C. Load side connection by tapping the feeder to the house within the meter main enclosure.

I want to be prepared when I submit the permit and grid connection applications in case I get pushback so any advice would be appreciated.
Click to expand...
I haven't seen anyone try to qualify a feedthrough bus using that rule, but I believe that whatever is on the other end of the feedthough should by at ;least the spirit of the rule contribute to the total breaker ratings on the bus.
 
That the proposal can be considered to comply with 705.12(B)(2)(3)(c) is a loophole that was (or was attempted to be) closed in the 2020 NEC. The proper application of the theory behind the 705.12(B)(2)(3)(c) would require counting the 200A main breaker in the house panel supplied by the subfeed lugs. So it would be unwise to apply 705.12(B)(2)(3)(c).

(B) is the proper solution. If you can't find the correct 175A main breaker, you could set a new panel with a 225A bus next to the meter main, supplied by the subfeed lugs, and move the 100A breaker and house panel supply over to it. Then a 60A breaker at the end of that 225A bus opposite its point of supply would comply with 705.12(B)(2)(3)(b).

Cheers, Wayne
 
ggunn said:
I haven't seen anyone try to qualify a feedthrough bus using that rule, but I believe that whatever is on the other end of the feedthough should by at ;least the spirit of the rule contribute to the total breaker ratings on the bus.
Click to expand...
Do you agree that with only the 100A breaker in the meter main that it is impossible for any part of the bus to see more than 200A?
 
wwhitney said:
That the proposal can be considered to comply with 705.12(B)(2)(3)(c) is a loophole that was (or was attempted to be) closed in the 2020 NEC. The proper application of the theory behind the 705.12(B)(2)(3)(c) would require counting the 200A main breaker in the house panel supplied by the subfeed lugs. So it would be unwise to apply 705.12(B)(2)(3)(c).

(B) is the proper solution. If you can't find the correct 175A main breaker, you could set a new panel with a 225A bus next to the meter main, supplied by the subfeed lugs, and move the 100A breaker and house panel supply over to it. Then a 60A breaker at the end of that 225A bus opposite its point of supply would comply with 705.12(B)(2)(3)(b).

Cheers, Wayne
Click to expand...
I am told the breaker is back-ordered to a factory in Mexico, and the next shipment scheduled (qty 500) is not sufficient to cover the current back-order quantity. There must be a lot of people with this Milbank getting solar installed with > 7.6k inverter. It may be easier to get a 150A breaker, but then the total capacity is really reduced.

This meter-main was installed when the outbuilding was built 2 years ago, and the homeowners are extremely sensitive to aesthetics. An additional 225A rated N3R panel next to the existing panel would likely be an eyesore to them. Those that I have seen have 30-42 spaces so it would be big, right?

One solution would be for Milbank (and other manuf) to increase the bus rating going forward on all 200A panels to 225A, to give headroom for solar. How much could a little more aluminum cost?

There are areas of the code that we come across with wording that does not make much sense in certain scenarios, but we usually have to live with them and often spend more time or money in the process. Here this situation seems like the code as it is written permits what I would like to do, unintended loophole or not, and from a practical sense it does not appear to present any danger/overcurrent situation as long as no more breakers are added to the meter main, which can be denoted using a placard. So can we not also take advantage of code wording when it helps us and also makes sense?
 
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solarken said:
Do you agree that with only the 100A breaker in the meter main that it is impossible for any part of the bus to see more than 200A?
Click to expand...
Not under the logic of 705.12(B)(2)(3)(c), which treats every breaker as if it could be a supply or a load, and doesn't consider the ordering of the breakers on the bus. So with a 200A utility supply breaker, and a 60A PV supply, and a 100A load and a 200A load, the bus could see 260A.

Now since you've interleaved the loads and supplies (if I understand correctly), no cross section of the bus can actually see more than 200A. But that gets into the territory of 705.12(B)(2)(3)(b), where again no cross section of the bus can see more than 200A, even with a 100% bus-size PV breaker at the opposite end of the bus. Yet the 120% limit applies due to concerns about overall heating within the panelboard enclosure. So by that logic, the 120% rule should apply to your interleaved proposal.

If you can get a 150A main breaker now, I suggest putting it in, which very likely won't cause any actual problems (i.e. trip on overload). Then you can put in the 175A main breaker if and when it is available and deemed necessary.

Cheers, Wayne
 
wwhitney said:
(B) is the proper solution. If you can't find the correct 175A main breaker, you could set a new panel with a 225A bus next to the meter main, supplied by the subfeed lugs, and move the 100A breaker and house panel supply over to it. Then a 60A breaker at the end of that 225A bus opposite its point of supply would comply with 705.12(B)(2)(3)(b).

Cheers, Wayne
Click to expand...
Wayne, would adding the 225A panel and moving the 100A breaker to it resolve this? I agree that the 225A panel fed by 200A from the service, and with a 60A PV backfed breaker would meet the 120% rule for that specific 225A panel, but the meter-main panel would be fed by the 200A service, and have a potential 60A source fed into it's bottom lugs from the 225A panel from the solar, assuming the house and outbuilding load is zero. So if someone added load breakers intor the meter main at a later time that exceeded 200A, then we are back to analyzing the current flow and specific positioning of breakers along the bus, no? I am not sure how this is different than my previous logic, that the key is to loudly proclaim via labeling that no additional breakers are permitted to be added to the meter main bus.
 
solarken said:
So if someone added load breakers intor the meter main at a later time that exceeded 200A
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Right, that wouldn't be allowed, and the meter main would be labeled as such. Counting the MB in the new 225A panel, it is already maxed out on 705.12(B)(2)(3)(c).

Cheers, Wayne
 
BTW, a "not compliant other than by loophole but to me should be compliant" option would be to interconnect your PV at the 100A feeder between the meter main and the outbuilding (ensure the outbuilding panel has a main breaker). That complies with the feeder interconnection rules.

If you treat the house main breaker as being in the meter main (as is appropriate for feed through lugs), then the arrangement of 3 connections to the meter main bus is not actually compliant with 705.12(B)(2)(3)(b) or (c). But with only 3 connections to the bus, it's not possible to overload the bus, as either one breaker is a supply and the other two are loads (the supply breaker protects the bus), or two breakers are supplies and the other is a load (the load breaker protects the bus).

So I submitted a PI for the 2023 NEC to expand 705.12(B)(2)(3)(c) in a way that would allow that (and other things; basically you would get to ignore one breaker of the smallest size present, based on a generalization of the above counting argument). However, it was rejected, presumably just on the basis that it is too complicated, even though correct on the physics.

Cheers, Wayne
 
wwhitney said:
BTW, a "not compliant other than by loophole but to me should be compliant" option would be to interconnect your PV at the 100A feeder between the meter main and the outbuilding (ensure the outbuilding panel has a main breaker). That complies with the feeder interconnection rules.
Click to expand...
Are you saying to tap the feeder between the 100A breaker and the outbuilding panel for the solar connection? From the perspective of the downstream outbuilding panel, if there was a 100A MB in it and it was rated for 100A, all good, sincce solar and/or grid would enter from the feeder. But from the meter-main perspective,wouldn't that look like a 200A utility source and a potential 60A PV source coming into a 200A rated bus in the meter main? Again it seems like we need to anlayze the current flow paths within the meter main bus.
 
Just out of curiosity, has it been ascertained that the bus in the existing meter-main panel bus is not rated for 225a?
 
solarken said:
Are you saying to tap the feeder between the 100A breaker and the outbuilding panel for the solar connection? From the perspective of the downstream outbuilding panel, if there was a 100A MB in it and it was rated for 100A, all good, sincce solar and/or grid would enter from the feeder. But from the meter-main perspective,wouldn't that look like a 200A utility source and a potential 60A PV source coming into a 200A rated bus in the meter main? Again it seems like we need to anlayze the current flow paths within the meter main bus.
Click to expand...
I'm not necessarily saying to do it, but yes that's the idea.

With only 3 connections to the meter main bus, if there were 260A of potential supply to the bus, there can only be 200A of load (the house panel). Likewise if the outbuilding breaker is a load, then there's only 200A of supply (the utility).

Cheers, Wayne
 
It's a bit off the wall, but have you looked at whether you can just eliminate all the branch OCPDs from the meter main? (I'm just brainstorming here, not really advocating this solution.)

You could use 4 port Polaris-style connectors to connect 200A pigtails from the feed through lugs; the 200A conductors to the house panel ; the 100A conductors to the outbuilding panel; and the PV conductors.

Looking just at the utility supply, the 100A feeder to the outbuilding and the PV conductors would need to comply with the feeder tap rules. 705.12(B)(2)(2) indicates the taps should be based on a source current of 200A plus 125% of the inverter output current. If the 100A feeder is outdoors only it might already comply with the outdoor unlimited length tap rule; otherwise a 100A disconnect would be required in an unobjectionable location that complies with the tap rules. The PV conductors would need a PV disconnect within the appropriate distance, with the conductors sized accordingly.

Then looking at 705.12(B)(2)(1), both the house panel and outbuilding panel would need main breakers.

I can't say that the above seems particularly safer than any of the previously discussed alternatives, but it seems to comply with all the rules both in spirit and letter. Implicit is that the Polaris connectors are rated for a higher current than the 200A bus.

Cheers, Wayne
 
solarken said:
This meter-main was installed when the outbuilding was built 2 years ago, and the homeowners are extremely sensitive to aesthetics. An additional 225A rated N3R panel next to the existing panel would likely be an eyesore to them. Those that I have seen have 30-42 spaces so it would be big, right?
Click to expand...
I only checked Square D's catalog, the smallest option I see there is a 12 space 3R main lug 225A panel, HOM12L225PRB, with dimensions 14.75" x 26" x 4.5".

Cheers, Wayne
 
wwhitney said:
If the 100A feeder is outdoors only it might already comply with the outdoor unlimited length tap rule; otherwise a 100A disconnect would be required in an unobjectionable location that complies with the tap rules.
Click to expand...
Thats a clever idea
 
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