Using feed thru lugs to feed a panel?

[tortuga]

Greetings group I have got a small residential PV system inverter to connect.
The house has a lot of panels, there is a 200A meter/main that feeds a empty main breaker outdoor 200A panel with feed thru lugs that feed a indoor panel main lug like so:

Utility---->Meter/200A main --->feeders--->200A 4 spot w/ feed thru Panel 3R ---> Indoor main lug panel.

I would like to land the PV breaker in the 200A 4 spot.
So it looks like my options are 705.12(B)(1)(a) OR 705.12(B)(1)(b)

I am wondering if I can just reverse the 200A 4 spot, land the feeder from the utility on the 'feed thru lugs' use the 200A breaker to feed the house panel? Seems like that would comply with 705.12(B)(1)(a) though it
might be a UL violation, I am going to look at the panel tomorrow and see what the sticker says.
I believe the conductors are 4/0 AL

Thoughts opinions?
Thanks in advance

 

[ggunn]

What is 125% of your maximum inverter output current? You know that you need to satisfy 705.12 in every panel between the PV interconnection and the utility, right?

 

[jaggedben]

I don't see how it works, unless you downsize a breaker.

(b) ( the 120% rule) does not work because your lugs and main breaker are at the opposite ends no matter how you switch them around, so you can't put the PV at one of those ends.

(a) only works if you downsize the utility breaker feeding the panel

As far as reversing the configuration of the middle panel, besides 110.(3)(B) (which might be ambiguous?) there's also the protection requirements in 408. I've always been unclear if this requires the breaker ahead of that panelboard, in part because I've so often seen installations that don't have it.

 

[wwhitney]

Some allowable options:

(a) if the middle panel has a busbar rating of 225A, and the inverter output current is no more than 20A, then the plan in the OP works. I don't see any 408.36 issues.

(b) just intercept the feeder from the meter main to the middle panel. If the meter/main doesn't have any space for distribution breakers, then you could interconnect up 160A of inverter current this way. Otherwise, you'd be limited by the 120% rule to 32A of inverter current this way, assuming the meter main has a 200A rated bus.

(c) replace the middle panel with a 200A (or 225A) MLO panel that accepts a 200A branch breaker and has room for an additional breaker for the PV. That lets the PV breaker be at the opposite end of the supply, and this way is good for 32A of inverter current (or 56A if the busbar is rated 225A).

Cheers, Wayne

PS As an aside, if in scenario in (c) the new panel has 8 spaces, and the 200A branch breaker takes up the right 4 spaces, and you want to interconnect two PV systems with two breakers in the left 4 spaces, does that still count as having the PV at the opposite of the bus as the supply? Since the upper left PV breaker is between the supply and half of the busbar connection of the 200A branch breaker.

 

[BradPV]

Couldn't he tap his feeder between the MSD and the second panel as long as he adds a fused disco within 10'. The OCPD before and after covers the conductor on both ends. This does have limitations to the load, so it depends on the PV load.

@wwhitney for your aside, why wouldn't you just relocate one of the branch breakers so the PV breaker could go at the bottom (opposite end)? I don't think stacking them would count since you would have a bus lower than the PV load.

 

[wwhitney]

@wwhitney for your aside, why wouldn't you just relocate one of the branch breakers so the PV breaker could go at the bottom (opposite end)? I don't think stacking them would count since you would have a bus lower than the PV load.

In the hypothetical, the panel has only 8 spaces, (2) columns of 4 each, and the 200A branch breaker takes up 4 spaces, all of one side. So it's not possible to put the (2) PV breakers at the bottom on both sides. If the panel were a lot bigger, you could raise the 4 space 200A branch breaker up from the bottom, although the ones I've seen would probably require you to leave a couple spaces below it empty to allow for extra wiring space.

Cheers, Wayne

 

[tortuga]

Thanks for the replies all, gives me stuff to ponder, I just got an update that the house panel does have a 200A main

(b) ( the 120% rule) does not work because your lugs and main breaker are at the opposite ends no matter how you switch them around, so you can't put the PV at one of those ends.

Siemens makes a lug kit I can put in the middle of the panel, I could feed the downstream house panel off that.
I could also remove the panel and intall a tap box and a 30A disco, there are no other breakers in there now.
However they might want that for future use.

What is 125% of your maximum inverter output current?

I believe its a Sunny Boy 5.0-US 21.0 Amp nameplate X 1.25 = 26.25 Max inverter output current

You know that you need to satisfy 705.12 in every panel between the PV interconnection and the utility, right?

I think the meter main is just that a meter with a main. Still need to get back to the site and check.

 

[tortuga]

So my updated info is this:
Utility---->Meter/200A main --->feeders--->200A 4 spot w/ feed thru Panel 3R ---> Indoor 200A main breaker panel.

 

[tortuga]

705.12(B)(3)(3) and 705.12(B)(3)(6) 2020 NEC

 

[BradPV]

In the hypothetical, the panel has only 8 spaces, (2) columns of 4 each, and the 200A branch breaker takes up 4 spaces, all of one side. So it's not possible to put the (2) PV breakers at the bottom on both sides. If the panel were a lot bigger, you could raise the 4 space 200A branch breaker up from the bottom, although the ones I've seen would probably require you to leave a couple spaces below it empty to allow for extra wiring space.

Cheers, Wayne

In that case I would just use a tandem breaker, skinny up in other words, that would keep you at the end of the bus. I have never tried to get one passed the way you explained but I think it would get push back fom most AHJ's, at least out east here.

 

[BradPV]

So my updated info is this:
Utility---->Meter/200A main --->feeders--->200A 4 spot w/ feed thru Panel 3R ---> Indoor 200A main breaker panel.

Maybe I'm missing something here but why wouldn't you just tie in with a 35A breaker in that middle panel? If you use a breaker you can use the 120% rule which gives you a 240a buss. If not that panel you can use the interior sub panel the same way. Most of our tie ins are on the inside panel as meter combos aren't all that common out here.

 

[wwhitney]

705.12(B)(3)(3) and 705.12(B)(3)(6) 2020 NEC

I would say the diagram does not comply with 2020 NEC 705.12(B)(3)(6). That requires "an overcurrent device . . . installed at the supply end of the feed-through conductors," to allow the use of 705.12(B)(3)(3) for the panel busbar. The meaning of that language is not very clear to me, but the diagram doesn't have anything that could match it. Maybe it means you are supposed to immediately hit a 200A OCPD just outside the panel with the feed-thru lugs.

Cheers, Wayne

 

[wwhitney]

Maybe I'm missing something here but why wouldn't you just tie in with a 35A breaker in that middle panel?

Because the feed-thru lugs are at the opposite end of the bus, so the 35A breaker wouldn't be? Up through the 2017 NEC, 705.12 was silent on this issue, and the most conservative interpretation was that you couldn't use the 120% rule on panels with feed-thru lugs. The 2020 NEC added 705.12(B)(3)(6), although the new language is somewhat unclear to me.

Cheers, Wayne

 

[tortuga]

Maybe I'm missing something here but why wouldn't you just tie in with a 35A breaker in that middle panel?

That's what I am proposing, the middle panel is the red T in the diagram. I had a 40A breaker on there 35 is probably correct size thanks.

 

[BradPV]

Because the feed-thru lugs are at the opposite end of the bus, so the 35A breaker wouldn't be? Up through the 2017 NEC, 705.12 was silent on this issue, and the most conservative interpretation was that you couldn't use the 120% rule on panels with feed-thru lugs. The 2020 NEC added 705.12(B)(3)(6), although the new language is somewhat unclear to me.

Cheers, Wayne

Okay, I'm reading this as the feed through lugs are protected by the supply side breaker. If that is true and the load side is protected in the next panel by a breaker 705.12 (3)(2) would apply allowing you to breaker tie the PV.

 

[BradPV]

That's what I am proposing, the middle panel is the red T in the diagram. I had a 40A breaker on there 35 is probably correct size thanks.

I feel that this is in compliance with NEC 705.12(3)(2) and is the process we follow almost daily. Though there are usually only 2 panels the same rules apply.

 

[tortuga]

Thanks for your input!
Kinda made my brain melt looking at 705 for too long and all these panels.

 

[BradPV]

Thanks for your input!
Kinda made my brain melt looking at 705 for too long and all these panels.

I get that lol. I see the 2017 reference on your tag line. The reference I gave was from 2020. 2017 reference is 705.12(B)(2)(3)(b).

 

[wwhitney]

Okay, I'm reading this as the feed through lugs are protected by the supply side breaker.

That doesn't match the language of 2020 705.12(B)(3)(6), which requires a breaker installed "at the supply end of the feed-through conductors." As the feed-through conductors start at the feed-through lugs, any OCPD on the bus upstream of the feed-through lugs would not match that description.

Cheers, Wayne

 

[wwhitney]

To be clear, I think the configuration in the diagram posted should be allowed by the NEC, as if the busbar in the panelboard were replaced with sections of 4/0 Al connected by 3 port Polaris connectors, it would comply with the feeder interconnection rules.

However, the NEC has stricter rules for busbars than wire-type feeders (possibly justified by the ease of adding more breakers) and the diagram does not comply with either 2017 or 2020 NEC 705.12.

Cheers, Wayne