Using feed thru lugs to feed a panel?

[tortuga]

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).

Thanks I gotta change that to 2020 LOL

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."

Hmmm the plot thickens.

 

[BradPV]

@wwhitney now that I've thought it over you are correct. The feed through lugs make this so that it doesn't work. Another catch is you then couldn't derate the feeder conductor so it would be undersized as well. Though if you go to the interior panel the breaker tie in works.

 

[tortuga]

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

Hmmm hold on I am reading 2020 705.12(B)(3)(6) like this

Connections shall be permitted on busbars of panel-boards that supply lugs connected to feed-through conductors.
The feed-through conductors shall be sized in accordance with 705.12(B)(1).

The next sentence "Where overcurrent device is installed at the supply end of the feed-though conductors … " does not apply.
So then I go to 705.12(B)(1) I can use (a) or (b)

 

[BradPV]

Hmmm hold on I am reading 2020 705.12(B)(3)(6) like this

Connections shall be permitted on busbars of panel-boards that supply lugs connected to feed-through conductors.
The feed-through conductors shall be sized in accordance with 705.12(B)(1).

The next sentence "Where overcurrent device is installed at the supply end of the feed-though conductors … " does not apply.
So then I go to 705.12(B)(1) I can use (a) or (b)

You would have to remove the feeder from the pass through lugs and put then on a breaker. The problem is your feeder going to the last panel can no longer be sized at 83% because it no longer supplies the entire premises wiring. You should be able to use the breaker tie in the last panel with the argument I made earlier before Wayne corrected me.

 

[tortuga]

Thanks I am starting to see the potential problem with this, no matter where you put the 35 or 40A inverter breaker as soon as they add another breaker they could overload the bus.

 

[wwhitney]

The next sentence "Where overcurrent device is installed at the supply end of the feed-though conductors … " does not apply.

The section is badly worded, but the intended meaning is clearly that where the above quoted sentence is not true, you may not use 705.12(B)(3)(1) through (3) to protect the panel busbar, and so the arrangement violates 705.12(B)(3).

Cheers, Wayne

 

[BradPV]

Thanks I am starting to see the potential problem with this, no matter where you put the 35 or 40A inverter breaker as soon as they add another breaker they could overload the bus.

Except in that last panel. There you only have to count the main breaker (200a) plus the PV breaker (35a) and using the 120% rule on the 200a bus you have 240a.

 

[tortuga]

 

[wwhitney]

Thanks I am starting to see the potential problem with this, no matter where you put the 35 or 40A inverter breaker as soon as they add another breaker they could overload the bus.

Actually if the 35A or 40A breaker is right next to the feed-thru lugs (at the bottom most position possible), then you can't overload the bus any more than you could with the normal 120% rule. That assumes the OCPD required by 705.12(B)(3)(6) right after the feed-thru lugs does not exceed the busbar rating (a specification missing from that section). 705.12(B)(3)(6) plus 705.12(B)(3)(2) basically becomes a version of the 120% rule where the second source is not at the opposite end of the bus, but is at the opposite end but one. Which is good enough.

Cheers, Wayne

 

[wwhitney]

Except in that last panel. There you only have to count the main breaker (200a) plus the PV breaker (35a) and using the 120% rule on the 200a bus you have 240a.

The last panel is supplied by only one source (one feeder), so 705.12 does not apply to it, and the above computation is not required.

Cheers, Wayne

 

[tortuga]

The last panel is supplied by only one source (one feeder), so 705.12 does not apply to it, and the above computation is not required.

Cheers, Wayne

I think Brad was suggesting I pipe over to that panel skip this middle one. Which is a good option.

 

[BradPV]

I think Brad was suggesting I pipe over to that panel skip this middle one. Which is a good option.

Exactly the PV is your second source now and you apply 705.12.

 

[tortuga]

Actually if the 35A or 40A breaker is right next to the feed-thru lugs (at the bottom most position possible), then you can't overload the bus any more than you could with the normal 120% rule. That assumes the OCPD required by 705.12(B)(3)(6) right after the feed-thru lugs does not exceed the busbar rating (a specification missing from that section). 705.12(B)(3)(6) plus 705.12(B)(3)(2) basically becomes a version of the 120% rule where the second source is not at the opposite end of the bus, but is at the opposite end but one. Which is good enough.

Cheers, Wayne

So are you thinking I can still use the middle panel? Just put the breaker at the bottom? It is in theory the same thing.

 

[LarryFine]

You would have to remove the feeder from the pass through lugs and put then on a breaker. The problem is your feeder going to the last panel can no longer be sized at 83% because it no longer supplies the entire premises wiring.

Remember, though, that the feeder conductors need not be larger than the service conductors.

 

[wwhitney]

I think Brad was suggesting I pipe over to that panel skip this middle one. Which is a good option.

I agree that if you can put a 40A PV breaker in the bottom panel at the end of the bus opposite the supply, you're good.

Cheers, Wayne

 

[wwhitney]

So are you thinking I can still use the middle panel? Just put the breaker at the bottom? It is in theory the same thing.

Yes, under the 2020 you can use the middle panel if you provide a breaker installed "at the supply end of the feed-through conductors." Which seems silly as there's already a 200A breaker at the other end of the feed-through conductors. IIRC the 2023 first draft changed the "supply end" language to be either end, which makes more sense.

Cheers, Wayne

 

[LarryFine]

Maybe someone will produce a panel with main breakers at both ends.

 

[tortuga]

Yes, under the 2020 you can use the middle panel if you provide a breaker installed "at the supply end of the feed-through conductors." Which seems silly as there's already a 200A breaker at the other end of the feed-through conductors. IIRC the 2023 first draft changed the "supply end" language to be either end, which makes more sense.

Cheers, Wayne

So your saying I would have to un-land the feed thru and slap a 200A breaker in the middle panel?
If there is a 2023 proposal I might be tempted to run this by AHJ and use 90.4,
I could always pipe to the other panel as Brad suggested.
Thank you all for your input!

 

[wwhitney]

So your saying I would have to un-land the feed thru and slap a 200A breaker in the middle panel?

Again, I don't know exactly what "where an overcurrent device is installed at the supply end of the feed-through conductors" means. I'm envisioning intercepting the 200A feeder just after the feed-thru lugs and adding a 200A enclosed circuit breaker.

Cheers, Wayne

 

[jaggedben]

Maybe this was already mentioned, but if you can manage to relocate the feed throughs to a breaker in the middle panel, then you could use the lugs to go to a fused disco of similar for the PV.