(2020) 705.12(B) and Bussed Gutters, Etc.

[wwhitney]

Does the phrase "distribution equipment . . . capable of supplying multiple branch circuits or feeders, or both" apply only to equipment that can contain OCPD?

Say you had a bussed gutter with 4 connections per bus (skipping over the case of 3 connections, as that does not allow for both multiple power source connections and multiple feeder connections). Is it subject to (2020) 705.12(B)?

If not, presumably instead a 6 position single phase MLO panelboard, with (3) sets of feed-thru lugs in the 6 positions, would be subject to 705.12(B). Since it is more "capable", because the feed-thru lugs could be replaced with OCPD?

Lastly, consider the Tesla Gateway 2 (an MID). It has busses, and those busses have 4 connections each (2 on the line side of the contactor, 2 on the load side of the contactor). Ignore the optional internal panelboard for the moment. Is it "distribution equipment . . . capable of supplying multiple branch circuits or feeders, or both"?

Cheers, Wayne

 

[ggunn]

I am a bit confused by 705.12(B)(1). I get that if we are tapping a feeder at other than the other end from the utility feed, the portion of the feeder between the tap and the other end needs to be protected by either increased conductor ampacity or OCP downstream from the tap, but what doesn't make sense to me is that the increased conductor ampacity must be "...not less than the sum of the primary source overcurrent protection device and 125% of the power-source output circuit current".

What about 240.4(B)? As written, 705.12(B)(1) seems to say that even if the inverter current is 0A the ampacity of the feeder must be not less than the rating of the OCPD protecting it. That makes no sense to me; shouldn't it read something like "...not less than the sum of the next standard size down OCP from the primary source overcurrent protection device and 125% of the power-source output circuit current"?

 

[jaggedben]

Does the phrase "distribution equipment . . . capable of supplying multiple branch circuits or feeders, or both" apply only to equipment that can contain OCPD?

Say you had a bussed gutter with 4 connections per bus (skipping over the case of 3 connections, as that does not allow for both multiple power source connections and multiple feeder connections). Is it subject to (2020) 705.12(B)?

Broadly speaking 705.21(B) would apply, although particular subsections would only apply to the components they mention. For example your bussed gutter would be subject to (1) and possibly (2) but not (3).

If not, presumably instead a 6 position single phase MLO panelboard, with (3) sets of feed-thru lugs in the 6 positions, would be subject to 705.12(B). Since it is more "capable", because the feed-thru lugs could be replaced with OCPD?

A panelboard by definition includes overcurrent devices, so a panelboard with feed through lugs in all positions isn't a thing. It would be sold as a bussed gutter. Also panelboards with more than one set of lugs without OCPD aren't really a thing in the actual market either. On commercial (bolt-on) panelboards it may be physically possible to put lugs in all the positions intended for breakers but that probably is not endorsed by the instructions.

Lastly, consider the Tesla Gateway 2 (an MID). It has busses, and those busses have 4 connections each (2 on the line side of the contactor, 2 on the load side of the contactor). Ignore the optional internal panelboard for the moment. Is it "distribution equipment . . . capable of supplying multiple branch circuits or feeders, or both"?

I'd say it clearly is capable of supplying multiple feeders, so in theory yes. However I presume it's also a listed assembly and AHJs usually allow listed assemblies to be used according to the instructions even where this contradicts a code section that might otherwise apply. The bussing would be considered factory installed internal wiring or construction of the listed assembly, see 2nd paragraph of 90.7.

 

[wwhitney]

Broadly speaking 705.21(B) would apply, although particular subsections would only apply to the components they mention. For example your bussed gutter would be subject to (1) and possibly (2) but not (3).

Sorry, why wouldn't section (3) on "Busbars" apply to a "bussed gutter"? I thought that was the whole difference between a "bussed gutter" and just a big junction box, that the bussed gutter has busbars.

A panelboard by definition includes overcurrent devices, so a panelboard with feed through lugs in all positions isn't a thing. It would be sold as a bussed gutter.

Good point. So if you take, say a HOM612L100 "main lug load center" and put in (3) HOML2125 plug-on subfeed lugs, what you've created is not an NEC panelboard. But that example is what I had in mind, so I should have said "load center" instead of "panelboard".

I'd say it clearly is capable of supplying multiple feeders, so in theory yes. However I presume it's also a listed assembly and AHJs usually allow listed assemblies to be used according to the instructions even where this contradicts a code section that might otherwise apply.

Good point, the 2023 NEC restricts 705.12(B) to "distribution equipment with no specific listing and instructions for combining multiple sources." So to the extent the Tesla GW2 has such specific listing and instructions (clearly it has the instructions, not clear on the listing), it would be exempt from 2023 705.12(B). But that doesn't address whether 2017 or 2020 705.12(B) should apply to the Tesla GW2 (beyond the idea that perhaps the 2023 language is an expression of what was intended all along).

The bussing would be considered factory installed internal wiring or construction of the listed assembly, see 2nd paragraph of 90.7.

This part I don't get--what distinguish that bussing from the bussing in a bussed gutter or in a panelboard?

Thanks,
Wayne

 

[jaggedben]

I am a bit confused by 705.12(B)(1). I get that if we are tapping a feeder at other than the other end from the utility feed, the portion of the feeder between the tap and the other end needs to be protected by either increased conductor ampacity or OCP downstream from the tap, but what doesn't make sense to me is that the increased conductor ampacity must be "...not less than the sum of the primary source overcurrent protection device and 125% of the power-source output circuit current".

What about 240.4(B)? As written, 705.12(B)(1) seems to say that even if the inverter current is 0A the ampacity of the feeder must be not less than the rating of the OCPD protecting it. That makes no sense to me; shouldn't it read something like "...not less than the sum of the next standard size down OCP from the primary source overcurrent protection device and 125% of the power-source output circuit current"?

It took me a minute to realize that what you're objecting to is the exclusion of applying 'next size up' rule. It seems common for code making panels to 'forget' about 240.4(B) when writing language for special situations. For example the way 240.21(B) is written you can't use the next size up to protect taps from overload either. Perhaps they are just afraid of too much word salad, which I'd say is a criticism that could be leveled at your solution. 705.12(B)(1) is already hard enough for the average person to understand.

Also another problem with your solution is that it should only apply at 800A or less, but 705.12(B)(1) needs to still apply at higher amps. (Maybe instead it should say 'the feeder conductor shall be protected by the sum of the ratings of primary source and power source overcurrent devices according to article 240'?)

 

[jaggedben]

Sorry, why wouldn't section (3) on "Busbars" apply to a "bussed gutter"? I thought that was the whole difference between a "bussed gutter" and just a big junction box, that the bussed gutter has busbars.

Ok, in the 2014 and 2017 versions that section applied to 'busbars in panelboards' and in 2020 they removed 'in panelboards' and I don't know exactly what their thinking was. I seem to recall there might have been a draft that wanted to add 'and switchboards' and maybe they thought that by making generic busbars they'd cover all the interesting cases, not thinking of your example.

Good point, the 2023 NEC restricts 705.12(B) to "distribution equipment with no specific listing and instructions for combining multiple sources." So to the extent the Tesla GW2 has such specific listing and instructions (clearly it has the instructions, not clear on the listing), it would be exempt from 2023 705.12(B). But that doesn't address whether 2017 or 2020 705.12(B) should apply to the Tesla GW2 (beyond the idea that perhaps the 2023 language is an expression of what was intended all along).

You assume something was intended all along. It might be more accurate to say that they are making explicit a widely accepted interpretation for when this question comes up. I'm glad to see it, as I have long thought (and said on this forum) that new panelboards should be able to be listed for interconnected power source arrangements beyond what the NEC has allowed.

This part I don't get--what distinguish that bussing from the bussing in a bussed gutter or in a panelboard?

The listing, especially the listing as an assembly. If you actually assembled components and tested them as an assembly under different scenarios, that's different than testing the one-way-at-a-time ampacity of a single busbar component with generic assumptions about what would enclose or protect it.

 

[ggunn]

It took me a minute to realize that what you're objecting to is the exclusion of applying 'next size up' rule. It seems common for code making panels to 'forget' about 240.4(B) when writing language for special situations. For example the way 240.21(B) is written you can't use the next size up to protect taps from overload either. Perhaps they are just afraid of too much word salad, which I'd say is a criticism that could be leveled at your solution. 705.12(B)(1) is already hard enough for the average person to understand.

You see what I am saying, right? Following the letter of the code, if you have a theoretical load side tap that contributes zero amps, the ampacity of the feeder must be equal to or greater than the OCPD rating, which we know is bogus.

Also another problem with your solution is that it should only apply at 800A or less, but 705.12(B)(1) needs to still apply at higher amps. (Maybe instead it should say 'the feeder conductor shall be protected by the sum of the ratings of primary source and power source overcurrent devices according to article 240'?)

Would that be problematic if both OCPDs are rounded up? I would keep the contribution by the tap at 125% of the inverter current but as you say, clarify the language to account for the case where the two sum to more than 800A.

I don't see that the writers of the NEC have been all that adverse to feeding us word salad; why should they start now?