NEC 250.122 - Size of EGC for 4,000A feeder

[infinity]

You're not reading 310.10(H) correctly. Look specifically at (1). No EGC's on that list.

(H)(5) EGC

I don't know what else to say, it says right there in bold what conductors are permitted to be paralleled. NO EGC's.

(H) Conductors in Parallel.
(1) General. Aluminum, copper-clad aluminum, or copper
conductors, for each phase, polarity, neutral, or grounded
circuit shall be permitted to be connected in parallel (elec-
trically joined at both ends) only in sizes 1/0 AWG and
larger where installed in accordance with 310.10(H)(2)
through (H)(6).

 

[Wire-Smith]

I don't know what else to say, it says right there in bold what conductors are permitted to be paralleled. NO EGC's.

"neutral or grounded circuit"

and (H)(5) is not in (H)(1) its a different section.

(H)(1) does not say nothing else except these can be paralleled

it says those shall be permitted, not "only these can be paralleled"

(H)(5) is actually expanding permissive language for cable segmented grounds, it is not more restrictive language, its more permissive.

 

[Wire-Smith]

besides an arbitrary code requirement why would you not allow paralleled grounds but you would ungrounded conductors? and please remember i believe you cannot use below 1/0 for paralleling.(except in cables)

 

[Wire-Smith]

edit.

i said go off 310 ampacity

310.10(H)(5)
segmented grounds, "combined circular mil area... complies with 250.122"

i would go with the larger of the two, if there not the same.

 

[infinity]

besides an arbitrary code requirement why would you not allow paralleled grounds but you would ungrounded conductors? and please remember i believe you cannot use below 1/0 for paralleling.(except in cables)

You're incorrect for the reasons that I've stated more than once, and we will have to agree to disagree.

 

[Wire-Smith]

You're incorrect for the reasons that I've stated more than once, and we will have to agree to disagree.

sounds good. i hope you didn't take anything i said as inflammatory it's very hard to convey tone on here, if you did i hope you don't refuse to consider my interpretation because of that. like i said before i believed your way for a long time, i understand why you think the way you do.


by the way i looked up 2014 250.122(f) old language and it does not change anything i said.


i am not trying to argue here,just having a discussion. but if you don't mind i asked "besides an arbitrary code requirement why would you not allow paralleled grounds but you would ungrounded conductors? and please remember i believe you cannot use below 1/0 for paralleling.(except in cables)"
in post 23, do you have a response to that?

i know i don't know everything and if i am wrong i would love and appreciate to be corrected.

 

[Wire-Smith]

OP i say only 1/0ALU is minimum required in each of the 12 sets.

looks like the largest way i have found is if you use the left column of 250.122/# of sets= current you go by in left column for parallel ground

it came out to #1

but as i said 1/0 is minimum for parallel


good luck trying to convince the ahj though.

 

[jaggedben]

I'm definitely with infinity. I don't see how you get around 250.122(F)(1)(b)

...The equipment grounding conductor installed in each raceway shall be sized in compliance with 250.122 based on the overcurrent device for the feeder or branch circuit ...

Emphasis added.

 

[Wire-Smith]

Fixing the quote would help.

However, since you have parallel conductors, "larger than the circuit conductor" would mean "larger than all 12 circuit conductors."

See 250.122(F).

then why would they say that "in no case shall they be required to be larger than circuit conductors"?
i am looking through the free air and high temp tables, i'm not seeing any very close to the 250.122 table

 

[Wire-Smith]

and i think CEC is vastly interpreted to allow parallel EGC

 

[Wire-Smith]

I'm definitely with infinity. I don't see how you get around 250.122(F)(1)(b)



Emphasis added.

one reason you need that in there, i just figured this out by running the numbers each way on how to come up with sizing for parallel ground. if you did like we talked about earlier (i was wrong) in using 310 you would come up with a smaller wire, you have to use that table it is based on cross sectional area not the ampacities in 310 (or at least not 310.15(B)(17) anyway)


310.10(H)(5)

segmented grounds in cables size off 250.122 circular mill area
they also use the term "complies with"

combined circular mil area of the sectioned equipment grounding conductors in each cable complies with 250.122

 

[Wire-Smith]

and i think CEC is vastly interpreted to allow parallel EGC

or at least in the way we are talking about (1 ground in each set) i don't have CEC i have just talked to them guys about this issue before.

 

[texie]

Wire-Smith, I'm afraid this is one that you will need to come around on. In the OP's situation the correct answer is 500CU or 750AL. This is well understood in the industry. While this has been the requirement for a long time, note that the language in 250.122(F)(1)(b) was new to the 2017 edition to make it even more clear.
But as I noted in my earlier post, this whole concept for sizing EGC is likely to go away in the 2020 edition.

 

[Wire-Smith]

Wire-Smith, I'm afraid this is one that you will need to come around on. In the OP's situation the correct answer is 500CU or 750AL. This is well understood in the industry. While this has been the requirement for a long time, note that the language in 250.122(F)(1)(b) was new to the 2017 edition to make it even more clear.
But as I noted in my earlier post, this whole concept for sizing EGC is likely to go away in the 2020 edition.

(f)(1)(b) is not new in 2017

i will ask again


"besides an arbitrary code requirement why would you not allow paralleled grounds but you would ungrounded conductors? and please remember i believe you cannot use below 1/0 for paralleling.(except in cables)"


it's only what you call "well understood in the industry" because of mindless parroting, someone wrote it somewhere and a lot of people just accepted it as gospel, this is not a good habit to get into, especially with electricity.

the base of this code section is possibly very old, i might look it up here before long. the "industry" often slowly forgets/misinterprets the intent of sections over the years. and i don't know how you get to speak for the industry, even code panel members argue on everything.

 

[infinity]

"besides an arbitrary code requirement why would you not allow paralleled grounds but you would ungrounded conductors? and please remember i believe you cannot use below 1/0 for paralleling.(except in cables)"

Paralleling ungrounded conductors is necessary paralleling EGC's is not. You cannot get a 4000 amp feeder without paralleling the ungrounded conductors.

I agree that requiring a full size EGC in each parallel raceway is just dumb but somewhere along the way someone thought that this was a good idea. We've been doing it that way for decades likely without much or any real science to back it up.

 

[Wire-Smith]

i would like to add just for a sidenote, i argue/have several opposing interpretations to code than many others on here and other forums other people on here can vouch for that, but the funny thing is this is the only one where i am arguing that a lower minimum is the correct interpretation, believe it or not.


again i ask

"besides an arbitrary code requirement why would you not allow paralleled grounds but you would ungrounded conductors? and please remember i believe you cannot use below 1/0 for paralleling.(except in cables)"



CEC i think would also allow something like the 1/0 in each of OP's sets, any CEC guys on here that can help us out?

 

[Wire-Smith]

Paralleling ungrounded conductors is necessary paralleling EGC's is not. You cannot get a 4000 amp feeder without paralleling the ungrounded conductors.

I agree that requiring a full size EGC in each parallel raceway is just dumb but somewhere along the way someone thought that this was a good idea. We've been doing it that way for decades likely without much or any real science to back it up.

i appreciate you trying to teach me. but then why would the cut-off point be 300 amps (2 sets of 1/0) you can get 300 without parallel.

and you can get unparalleled 4000 amp feeder with bus, but i know what your saying (wire type). i say thats a decent arguement, but then why not allow how op interpreted " does not need to be larger than ungrounded conductors"


i do not want to bug you anymore if i am, i just offer a friendly suggestion to consider what i am saying, not take it for the truth because i am saying it, but consider it and look at the code. i know you will likely not change your mind, i am honestly just trying to offer a helpful suggestion. like i said before, i used to interpret it the same way you did and i even corrected people and told them that way was required

 

[texie]

(f)(1)(b) is not new in 2017

I would suggest you check this.

 

[Wire-Smith]

I would suggest you check this.

ahh, thanks for the suggestion, its not shaded, but i agree its re-formatted. yep i need to get to bed. Thank You. I overlooked the (N)

i think it says the same thing in meaning though, but i am tired i will read them both again tomorrow, thank you

 

[Wire-Smith]

i found a cmp statement on this (which is incorrect) that refutes the parallel sizing part (not the larger than circuit conductor part).

they said the fault current will take the ground closest to the fault, that wire will get too hot and melt. this is the old flawed logic that current takes the path of least resistance. the larger proportion will take that wire but as that wire heats up its impedance will increase and therefore the other wires will begin to take more of the current(not like you would likely be able to measure this with instruments it would probably instantly look like all of the grounds carry close to the same amount of current). the current will take all available paths proportional to impedance's. this was 1983 comments, i'm still looking.

in another proposal comment(i will try to find it again) the panel voted against a requirement for short circuit current limiting sizes of parallel conductors and there reasoning was fault current is divided among all the conductors, lol.