Thank you for all the info!It only needs sized per the load it will carry though that can be a little tricky to calculate. But if you have a panelboard with all line to line loads other than say a lighting circuit and maybe a general purpose receptacle circuit or two then it becomes rather obvious the max load on that neutral will be limited to what comes from just those few single pole circuits.
Services do limit the minimum size to be same as the minimum supply side bonding jumper size even if calculated load is less.
Feeders do limit the minimum size to be same as the minimum equipment grounding conductor size even if calculated load is less.
I think many AHJ's will allow reduction in most cases to not exceed two conductor sizes without needing to give any kind of load calculation. Lots of cables or multiplexed conductor assemblies do come with a neutral that is two sizes smaller than the ungrounded conductors.
It only needs sized per the load it will carry though that can be a little tricky to calculate. But if you have a panelboard with all line to line loads other than say a lighting circuit and maybe a general purpose receptacle circuit or two then it becomes rather obvious the max load on that neutral will be limited to what comes from just those few single pole circuits.
Services do limit the minimum size to be same as the minimum supply side bonding jumper size even if calculated load is less.
Feeders do limit the minimum size to be same as the minimum equipment grounding conductor size even if calculated load is less.
I think many AHJ's will allow reduction in most cases to not exceed two conductor sizes without needing to give any kind of load calculation. Lots of cables or multiplexed conductor assemblies do come with a neutral that is two sizes smaller than the ungrounded conductors.
If you can prove the neutral load is no more than ampacity of the 8 AWG why not? This is the smallest it can be regardless what your calculation is though. If there is a significant amount of 240 volt loads neutral load could easily be low.Given what you said would you think it code compliant to run a 100 ampere dwelling unit feeder as Two # 4 AWG energized, one 8 AWG Grounded Conductor, and one #8 Equipment Grounding Conductor? I just spent a couple of hours on 215.2(A)(1) and the table in 250.122 and I cannot seem to get it clear in my head. Bad day I guess.
Do you have a code citation for that last statement?If you can prove the neutral load is no more than ampacity of the 8 AWG why not? This is the smallest it can be regardless what your calculation is though.
Do you have a code citation for that last statement?
Thanks,
Wayne
215.2(B)
(B) Grounded Conductor.
The size of the feeder circuit grounded conductor shall not be smaller than the equipment grounding conductor size required by 250.122, except that 250.122(F) shall not apply where grounded conductors are run in parallel.
Additional minimum sizes shall be as specified in 215.2(C) under the conditions stipulated.
More a case of I knew it and then forgot it. @jaggedben, didn't this question come up recently in a different thread? See 215.2(B).I am certain you know this but not sure what you are getting at.
More a case of I knew it and then forgot it. @jaggedben, didn't this question come up recently in a different thread? See 215.2(B).
Cheers, Wayne
Ah, yes. There it is! Also a case of I knew and forgot. Was looking in the wrong places for it.
That other thread was this one.
Article 240 and Grounded Conductors
Say I have a 240V 3P3W corner grounded system, and I use panelboards with just 2 busbars for the ungrounded conductors along with a terminal bar for the grounded conductors. OCPD is appropriately rated 240V to ground. Now I install a 2 pole 40A breaker with (2) #8 Cu ungrounded conductors, a...forums.mikeholt.com
Yes that is the crux of the matter isn't it. With a clothes dryer, 240 volt portion of the kitchen range, water heater I was guessing that the neutral current might actually be less than 70. If I'm allowed to multiply that by the 83% dwelling unit factor it might actually make it to #8 AWG. But I think #6 is more likely. I suspect I'd have to run it in non metallic flexible conduit fully enclosed in 1/2 inch sheet rock to be able to run the 2 #4 AWG, 1#6AWG, and 1 #8 AWG that is the more likely result of the calculation. 4-4-4-8 cable is much more likely to be available then 4-4-6-8 would be. So I'd have to compare the cost of the 2 methodologies to see which one was worth doing.If you can prove the neutral load is no more than ampacity of the 8 AWG why not? This is the smallest it can be regardless what your calculation is though. If there is a significant amount of 240 volt loads neutral load could easily be low.
The text of 2023 NEC 310.12(A), for example, is:Yes that is the crux of the matter isn't it. With a clothes dryer, 240 volt portion of the kitchen range, water heater I was guessing that the neutral current might actually be less than 70. If I'm allowed to multiply that by the 83% dwelling unit factor it might actually make it to #8 AWG.
Given what you said would you think it code compliant to run a 100 ampere dwelling unit feeder as Two # 4 AWG energized, one 8 AWG Grounded Conductor, and one #8 Equipment Grounding Conductor? I just spent a couple of hours on 215.2(A)(1) and the table in 250.122 and I cannot seem to get it clear in my head. Bad day I guess.
I don't think that is a valid because the language change that clarified that the supply conductors must be supplying the entire load was to put a stop to the practice of running 2 different feeders from the Service Equipment to 2 different panels in large new homes and applying the reduced sizing to different sets of conductors. The formal interpretations made by the NFPA on the issue previously were clear that was a misapplication of the reduced size allowed for feeders. Contractors were taking advantage of the misunderstood allowed reduction in sizing, which had been taken verbatim from the allowable reduction in size for the service, which in the situation I'm describing is fully compliant, and applying that to 2 and more feeders to separate parts of the load.Concurring with @wwhitney : IMHO the 83% factor for a residence doesn't apply to your neutral calculations, since they by default are only a portion of the residence load.
True, but not everyone uses a cable at all times. They do make raceways and individual conductors.Thanks wwhitney
I appreciate the help. That makes the whole thing simpler. 4-4-4-8 cable will be a lot simpler to find than 4-4-6-8 would ever be.
Tom Horne
I agree. I also likely would seldom or never run 8 AWG neutral with a 100 amp feed to a dwelling unit. Feeder within a dwelling - maybe, would depend on what the supplied loads are.If the calculated neutral current is low enough, the #8 would suffice.
I don't think the #4s would work for the hots, unless this 'feeder' is carrying the entire load of the residence or the residence only has a 100A service with #4 conductors.
Concurring with @wwhitney : IMHO the 83% factor for a residence doesn't apply to your neutral calculations, since they by default are only a portion of the residence load.