EGC--------Quiz

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For other than paralleled conductors none. However if you parallel conductors and you lose a ground in one set the ground in the other set will be sized large enough to provide the ground protection per the overcurrent device.
 
Post 15
don_resqcapt19 said:
The circuit conductor is not the conductor in each raceway...it all of the individual conductors that are connected in parallel. The code requires a 800 kcmil in each raceway, no matter how big or small the individual conductors that make up the circuit conductor are.
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don_resqcapt19 said:
I think he was after what I said in post 15.
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That's where I was going:smile:......Although not a very common installation in my neck of the woods.....I'm sure its out there, and could really bite ya in the back pocket (the one where all the money was), if you had to correct the violation due to improper EGC sizing.......

It seems that you would be okay if Pierre C Belarge was your inspector:rolleyes::wink::grin:
 
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necplus.org

necplus.org

necplus.org Staff Note for 250.122(F)

Where conductors are run in parallel raceways or cables as permitted by 310.4, each parallel equipment grounding conductor shall be sized per Table 250.122 based on the size of the overcurrent device protecting the conductors. In other words, the equipment grounding conductor in each raceway or cable must be full-sized, even though the ungrounded (phase) conductors are reduced in size.
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I pulled this from necplus.org http://www.necplus.org/Pages/Default.aspx
 
My mind is open to this discussion.
I would like someone to explain to me why (electrically speaking) the equipment ground conductor is required to be larger than the ungrounded conductor.

As I see it, the size of the ungrounded conductor will restrict/determine how much current will flow in the fault current path, during a ground fault. Increasing the size of the EGC serves what purpose?
 
I was taught as Pierre says, the EGC does not need to be larger that the size of a single conduit phase conductors. But open to see more on this (OF COURSE).
 
ibew501ed said:
I don't see anything on this link to help clarify??:-?
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Sorry:smile:.....Originally I tried a link to the exact page, but it did not work right because one would have to subscribe to necplus.org in order to view the staff note I posted. It is a pretty good code searching tool and also has all kinds of good info on there.....I think you can try it free for a day and if you like it its about 10 bucks a month.
 
The NEC Says So!

The NEC Says So!

Pierre C Belarge said:
My mind is open to this discussion.
I would like someone to explain to me why (electrically speaking) the equipment ground conductor is required to be larger than the ungrounded conductor.
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Thats easy:smile: We all have to answer to an authority, the NFPA is the authority......and it is written...

250.122(F) Conductors in Parallel.
Where conductors are run in parallel in multiple raceways or cables as permitted in 310.4, the equipment grounding conductors, where used, shall be run in parallel in each raceway or cable.

Each parallel equipment grounding conductor shall be sized on the basis of the ampere rating of the overcurrent device protecting the circuit conductors in the raceway or cable in accordance with Table 250.122.
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necplus.org(not a formal interpretation) said:
Staff Note for 250.122(F)
Where conductors are run in parallel raceways or cables as permitted by 310.4, each parallel equipment grounding conductor shall be sized per Table 250.122 based on the size of the overcurrent device protecting the conductors. In other words, the equipment grounding conductor in each raceway or cable must be full-sized, even though the ungrounded (phase) conductors are reduced in size.
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I can see this being read either way. There is no solid code support for either interpretation of the interaction between 250.122(A) and .122(F). Without a code clarification, it is my reading that the sum of all of the conductors in parallel is the circuit conductor for the purposes of the application of 250.122(A).
 
don_resqcapt19 said:
I can see this being read either way. There is no solid code support for either interpretation of the interaction between 250.122(A) and .122(F). Without a code clarification, it is my reading that the sum of all of the conductors in parallel is the circuit conductor for the purposes of the application of 250.122(A).
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I was under the understanding, that the overcurrent device was how we determined the size of the EGC, not the size of the conductors.

I am not too sure if I actually understand what you may be trying to tell us/me.
 
Pierre C Belarge said:
My mind is open to this discussion.
I would like someone to explain to me why (electrically speaking) the equipment ground conductor is required to be larger than the ungrounded conductor.

As I see it, the size of the ungrounded conductor will restrict/determine how much current will flow in the fault current path, during a ground fault. Increasing the size of the EGC serves what purpose?
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If you have parallel conductors in two raceways and you lose one grounding conductor the other grounding conductor will be sized large enough to satisfy the requirements of table 250.122.
 
Pierre C Belarge said:
I was under the understanding, that the overcurrent device was how we determined the size of the EGC, not the size of the conductors.

I am not too sure if I actually understand what you may be trying to tell us/me.
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Pierre,
I am saying that for the purposes of the rule in 250.122(A) that says the EGC is not required to be larger than the circuit conductors, that the sum of all of the conductors in parallel is the circuit conductor, not the individual conductor in a single raceway. The EGC is sized by T250.122 and the rating of the OCPD. In this example the rule in 250.122(F) would require a 800 kcmil EGC in each raceway, no matter what size the phase conductors in that raceway are.
 
I really liked this brain teaser, but need practicality

So how this for a more realistic example?

I have 1600 amp bus and want to do a tap to a 400 amp C/B

I use parallel 3/0 conductors and keep the wire length to 10 feet and two seperate conduits.

I would then have to use a 4/0 EGC in each conduit.
 
don_resqcapt19 said:
Pierre,
I am saying that for the purposes of the rule in 250.122(A) that says the EGC is not required to be larger than the circuit conductors, that the sum of all of the conductors in parallel is the circuit conductor, not the individual conductor in a single raceway. The EGC is sized by T250.122 and the rating of the OCPD. In this example the rule in 250.122(F) would require a 800 kcmil EGC in each raceway, no matter what size the phase conductors in that raceway are.
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Don
I respect your vast knowledge of the NEC. Its certainly much greater that mine. Your quote of 250.122(A) says
250.122(A) that says the EGC is not required to be larger than the circuit conductors. Circuit conductors Plural and not Circuit conductor singular. The circuit conductors in this case are 500 kcm.
It makes sense that the EGC would not be required to be larger that 500 kcm as Mr Piierre as said.
 
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LarryFine said:
Larry, just use the conduit. :cool:
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I'm good with that unless it is PVC.

The othe rinspector I work with has a job where a 2500 amp C/B feeds a meter center. 10 runs of 750 kcmil AL with a 900 kcmil AL EGC in each. The 750 is oversised for V.D. and the EGC is bumped as well.

Section 250.122(A) is titled "General". That tells me that the following subsections modify the general rule, just like in other areas of the code. So subsection (F) would prevail.
 
bob said:
Don
I respect your vast knowledge of the NEC. Its certainly much greater that mine. Your quote of 250.122(A) says
250.122(A) that says the EGC is not required to be larger than the circuit conductors. Circuit conductors Plural and not Circuit conductor singular. The circuit conductors in this case are 500 kcm.
It makes sense that the EGC would not be required to be larger that 500 kcm as Mr Piierre as said.
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Bob,
It is my opinion that the plural is for the fact that there is more than one ungrounded conductor in many circuits. It is also my opinion that all of the conductors that make up phase A is a single circuit conductor for the purposes of 250.122(A). In the case of the 500's that would make the circuit conductors 8,000 kcmil and the 800 kcmil is only 10% of that. I may very well be all wet on this one, but that is how I read it. As I said, I don't see any solid code support for either your reading or my reading of this code section.
 
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