Parallel EGC

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electrofelon said:
So why do they say you can run egc's in parallel, when you actually can't :?
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ActionDave said:
They are in parallel. If you didn't parallel them you would have one lonely EGC in one pipe. You just aren't allowed to combine more than one smaller EGC to increase the ampacity.,
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When different branch circuits, smaller than 1/0 AWG, are present in a junction box on a raceway wiring method, we are required to bond all the EGCs together, without any conditions for increasing the size of the smaller EGCs. We are directed to create an "effective ground-fault current path." The smaller AWG EGCs are fine connected to the larger AWG EGCs with no concern for the rating of the largest OCPD.

The strict interpretation of 310.10(H)(5) in this thread is in conflict with the rest of the rules elsewhere in the Code. . . in my opinion.
 
According to the Soares book on grounding, "one reason for a full size conductor in each raceway is that if a line to ground fault occurs in the raceway, current will be fed tom the fault from both directions. The equipment grounding conductor will thus be called upon to carry the entire amount of the fault current".
I have no idea if that adds clarity.
 
augie47 said:
According to the Soares book on grounding, "one reason for a full size conductor in each raceway is that if a line to ground fault occurs in the raceway, current will be fed tom the fault from both directions. The equipment grounding conductor will thus be called upon to carry the entire amount of the fault current".
I have no idea if that adds clarity.
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I get that but why wouldn't a equivalent parallel equipment grounding conductor do the same.
 
Dennis Alwon said:
I have not seen definitive proof of this. I think the verdict is still out afaik.
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310.10(H) does not say anything about equipment grounding conductors, only phase and grounded/neutral conductors.

250.122(A)....egc of wire type shall not be smaller than shown in table 250.122

250.122(A)(1)... egc size shall not be smaller than determined by 250.122(A) based on the rating of the branch circuit short circuit and ground fault protective device.

And the last sentence of 250.122(F) Conductors in Parallel .... Each egc shall be sized in compliance with Table 250.122

Table 250.122 is the minimum size for egc's. You can't go smaller.
 
I dont like it. They are saying "you can parallel egc's" but only in a way that isnt really paralleling (in the sense of why we do it). Im not sure if the section is just poorly written or intends that we can parallel (divide a single EGC into multiple smaller ones).
 
al hildenbrand said:
When different branch circuits, smaller than 1/0 AWG, are present in a junction box on a raceway wiring method, we are required to bond all the EGCs together, without any conditions for increasing the size of the smaller EGCs. We are directed to create an "effective ground-fault current path." The smaller AWG EGCs are fine connected to the larger AWG EGCs with no concern for the rating of the largest OCPD.
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You always have to have a full size ground based on the largest OCPD.

The strict interpretation of 310.10(H)(5) in this thread is in conflict with the rest of the rules elsewhere in the Code. . . in my opinion.
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No it isn't. The first sentence says ....they shall be size in accordance with 250.122.
 
infinity said:
Let's assume that you can do something like this, please show me where the calculation for for finding the equivalent size of the single EGC is in the NEC.
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parallel conductors are electrically joined at both ends to form a single conductor


Based on the circular mill area of a single conductor
 
al hildenbrand said:
Is 310.10(H)(5) relevant to this topic?
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Yes. And the first thing it says, tough not in so many words, is that if you pull an egc in conduit it has to be sized according to 250.122.

The second thing it says, not in so many words, is that if have some kind of fancy cable assembly, ie, mc or se that has some weird multi stranded egc inside the cable that's ok because it's part of a manufactured product. This is not unique, the code treats cable assemblies and conductors in raceways different in other sections.
 
I do believe at this stage that the intent is to not allow the install I stated in the opening post, however, I do believe it needs to be written better. The other question is why??? I assume it because they don't want to rely on a parallel run being perfect so that the fault will clear.
 
Dennis Alwon said:
I do believe at this stage that the intent is to not allow the install I stated in the opening post, however, I do believe it needs to be written better. The other question is why??? I assume it because they don't want to rely on a parallel run being perfect so that the fault will clear.
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Why do you have to pull a full size green in a metal conduit? Why do you have to tie all the egc's from separate circuits together when they are in the same box? Why is 250.122(B) still in the code book even though it makes no sense. It's all part of this ritualistic attitude that surrounds grounding.
 
Dennis Alwon said:
If I have to parallel my conductors to be sized at 800 kcm(490 amps). If I want to parallel them I could use 2- 250(255*2=510amps)

Now suppose by equipment grounding conductor in a different example needs to be 500 kcm based on 250.122. Do I use Table 8 and use 2-250 kcm or do I use table 310.15(B)(16) as done above for the ungrounded conductors assuming a 75C rating. Thus 500 kcm(380 amps) so I could use 2- 3/0 (200 *2=400 amps).

I feel I should know this. In this example I want to parallel the equipment grounding conductor in one conduit
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Why would you want to do this? It's more expensive and the conduit size may have to be increased. Its A-Typical installation is why you are having problems working it to the code sections.

As long as the EGC was capable per code to trip the breaker, I would not fail it in an inspection. Now trying to pretzel my way to see if I can get the codebook to concur, that is a different matter.
 
Gary11734 said:
Why would you want to do this? It's more expensive and the conduit size may have to be increased. Its A-Typical installation is why you are having problems working it to the code sections.

As long as the EGC was capable per code to trip the breaker, I would not fail it in an inspection. Now trying to pretzel my way to see if I can get the codebook to concur, that is a different matter.
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Well, I don't.. this is hypothetical but can you imagine pulling a 1200 kcm wire instead of 2-600 kcm conductors. The cost there may be significant as no one stocks 1200 kcm wire
 
Dennis Alwon said:
Well, I don't.. this is hypothetical but can you imagine pulling a 1200 kcm wire instead of 2-600 kcm conductors. The cost there may be significant as no one stocks 1200 kcm wire
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If its hypothetical, I see no reason why you couldn't do it. If it will trip the breaker, then OK in my book.

It sounds like you have a good idea when it comes to the bigger sizes...
 
ActionDave said:
310.10(H) does not say anything about equipment grounding conductors, only phase and grounded/neutral conductors.
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al hildenbrand said:
Is 310.10(H)(5) relevant to this topic?
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ActionDave said:
Yes.
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OK.

Look at 310.10(H)(1), where the "nothing smaller than 1/0 limitation" occurs and you will note that EGCs are NOT subject to the limitation. From Table 250.122 we read there are nine AWG sizes SMALLER than 1/0, all the way to, and including, # 14.

Looking at 310.10(H)(5) one cannot read a size limit for paralleled EGCs.

More importantly, 310.10(H)(5) places NO additional conditions on what must accompany paralleled EGCs. It says "Where parallel EGCs are used. . . " Parallel EGCs are NOT required to be part of parallel phases or neutrals, etc. An EGC can be paralleled by itself.

So, again, here's my problem.

Please consider: An occupancy is wired with a Nonmetallic Raceway Method. A 20 Amp OCPD #12 branch circuit with wire-type EGC is run in Nonmetallic Raceway to a bank of switches in a single multigang box. A 15 Amp OCPD #14 branch circuit with a wire-type EGC is run in a different Nonmetallic Raceway to the same bank of switches. The EGCs in the #12 and #14 home runs are in parallel, and, by 310.10(H)(5)and Table 250.122, the EGC for the #14 homerun has to be #12 . . .
 
al hildenbrand said:
OK.

Look at 310.10(H)(1), where the "nothing smaller than 1/0 limitation" occurs and you will note that EGCs are NOT subject to the limitation. From Table 250.122 we read there are nine AWG sizes SMALLER than 1/0, all the way to, and including, # 14.

Looking at 310.10(H)(5) one cannot read a size limit for paralleled EGCs.

More importantly, 310.10(H)(5) places NO additional conditions on what must accompany paralleled EGCs. It says "Where parallel EGCs are used. . . " Parallel EGCs are NOT required to be part of parallel phases or neutrals, etc. An EGC can be paralleled by itself.

So, again, here's my problem.

Please consider: An occupancy is wired with a Nonmetallic Raceway Method. A 20 Amp OCPD #12 branch circuit with wire-type EGC is run in Nonmetallic Raceway to a bank of switches in a single multigang box. A 15 Amp OCPD #14 branch circuit with a wire-type EGC is run in a different Nonmetallic Raceway to the same bank of switches. The EGCs in the #12 and #14 home runs are in parallel, and, by 310.10(H)(5)and Table 250.122, the EGC for the #14 homerun has to be #12 . . .
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it may be slipping my mind, but what code section states the equipment grounds at the multi gang box have to all be pigtailed together
 
david said:
it may be slipping my mind, but what code section states the equipment grounds at the multi gang box have to all be pigtailed together
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It's been awhile since I've looked it up. I believe 250.148 is the appropriate citation.
 
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