250.122(a)

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Dennis Alwon

Dennis Alwon

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I guess I should have asked before I sent in a proposal but do you think that 250.122 (A) should be rewritten.

It states, in no case shall the egc be required t be larger than the circuit conductors. If we install 7 conduits with1/0 conductors on a 1000 amp breaker then the egc is required to be 2/0 in each conduit. Do you all agree or disagree with me?
 
Tree limbs are everywhere...

I disagree, one addresses the circuit in that conduit, or service for that run of conduit, not the end result of the size of the service. One is meeting that requirement of the Service with the quantiy mass of the wire in seven conduits.

There's another place in the Code where the wire size of EGC drops per the quantity of the size of the circuits to the service IN THAT one conduit.

I'm missing the argument, D!

What about the other code articles it list ?
 
Part of the problem is using the fact that you #1/0 in each raceway when in fact the 1000 amps worth of conductors are in all 7 raceways in parallel. IMO you would need a #2/0 EGC. I see no exception for the EGC not being required to be larger than the circuit conductors in the raceway in 250.122(F).

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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Why would you want to add more code to the NEC for an installation that would probably never happen anyways?

Have you ever heard/seen 7 parallel 1/0's?

I'm all for more code clarity, but not when it's unrealistic examples cooked up for no other reason than "what if?"

That'll just make the book thicker than it already is....
 
Apparently it has come up although a rarity. The fact is the book is incorrect and , IMO needs correcting.

Also there are many contractors who believe the egc would not need to be 2/0 and I believe they be wrong.

It is a minor point but I needed something to gripe about. :grin: I wrote the proposal-- we'll see. Just wanted to know if you all agree that 2/0 is needed in that unusual situation.
 
Dennis Alwon said:
It is a minor point but I needed something to gripe about. :grin: I wrote the proposal-- we'll see. Just wanted to know if you all agree that 2/0 is needed in that unusual situation.
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I agree, for this hypothetical installation, #2/0's.
 
Dennis Alwon said:
I guess I should have asked before I sent in a proposal but do you think that 250.122 (A) should be rewritten.

It states, in no case shall the egc be required t be larger than the circuit conductors. If we install 7 conduits with1/0 conductors on a 1000 amp breaker then the egc is required to be 2/0 in each conduit. Do you all agree or disagree with me?
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Dennis,

IMO, This is only one circuit not seven, therefore 2/0 is not larger than the circuit conductors. yes/no ?
 
Dennis Alwon said:
The 2/0 is in all 7 conduits as is the 1/0. I don't follow what you're saying.
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He saying that since there are 7 sets in parallel the circuit condcutors are actually, 7 X 1/0, therefore the 2/0 in each raceway is still smaller than the circuit conductors.
 
infinity said:
He saying that since there are 7 sets in parallel the circuit condcutors are actually, 7 X 1/0, therefore the 2/0 in each raceway is still smaller than the circuit conductors.
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I see that but it is also 7* 2/0..... The total cm in the end is a larger egc.
 
Dennis Alwon said:
I see that but it is also 7* 2/0..... The total cm in the end is a larger egc.
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The NEC doesn't seem to care about that. If you put seven sets in one raceway (think a wireway) you would only need one EGC sized according to 250.122. If you use seven raceways you'll need seven EGC's.
 
infinity said:
The NEC doesn't seem to care about that. If you put seven sets in one raceway (think a wireway) you would only need one EGC sized according to 250.122. If you use seven raceways you'll need seven EGC's.
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I understand that. My point being that the ground fault that may occur must be capable of tripping the breaker hence the need for 2/0 in all the conduits. There are many ec's that believe that they would only need 1/0 in each conduit because of the way 250.122(A) is written.

When we were in Raleigh a contractor was adamant that it did not need to be larger than 1/0 but the code panel straightened him out. I totally understand what's going on but many ec's don't get the picture. Some think the egc run in parallel only need to have a total cm equivalent of 2/0.
 
infinity said:
The NEC doesn't seem to care about that. If you put seven sets in one raceway (think a wireway) you would only need one EGC sized according to 250.122. If you use seven raceways you'll need seven EGC's.
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I've always disagreed with the need for a full size egc in each conduit of parallel sets.
 
Dennis Alwon said:
I understand that. My point being that the ground fault that may occur must be capable of tripping the breaker hence the need for 2/0 in all the conduits. There are many ec's that believe that they would only need 1/0 in each conduit because of the way 250.122(A) is written.
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IMO when using parallel feeders 250.122(F) applies not 250.122(A). Maybe a proposal that stated 250.122(A) does not apply to parallel feeders would be helpful.
 
In the example that Dennis has given I don't see the reason, electrically speaking, that the EGC must be larger than the hot conductors. If there were a ground fault in one out of the seven raceways the size of the ungrounded conductor in that raceway would limit the amount of current. If the ungrounded conductor is 1/0 why would the EGC need to be larger (of course, other than the NEC making it mandatory)?

Pete
 
pete m. said:
In the example that Dennis has given I don't see the reason, electrically speaking, that the EGC must be larger than the hot conductors. If there were a ground fault in one out of the seven raceways the size of the ungrounded conductor in that raceway would limit the amount of current. If the ungrounded conductor is 1/0 why would the EGC need to be larger (of course, other than the NEC making it mandatory)?

Pete
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It has to do with breaker size not just wire size. 1/0 would probably work in most cases but so would a #10 wire probably.
 
pete m. said:
If the ungrounded conductor is 1/0 why would the EGC need to be larger (of course, other than the NEC making it mandatory)?
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Because the fault current will flow into the fault point from the other six conductors as well. I see your point, that all of the fault current has to flow into that single 1/0 that has the fault condition. But there is a difference between the amount of current that will flow from a single circuit consisting of one set of 1/0's and a parallel circuit consisting of seven sets of 1/0's.
 
Dennis, I don't see an ambiguity here. Let me invite your attendtion to the fact that 250.122(A) does not say that the EGC need not be larger than the circuit conductors in the same raceway. It says the EGC need not be larger than the circuit conductors supplying the equipment. In your example, the circuit conductors supplying the equipment consist of seven 1/0's, so the EGC need not be larger than that. I think the present wording is clear enough, provided that the reader read all the words. Charlie's Rule wins again! :cool:
 
Dennis,

So what was your proposal? I agree that current code would require a 2/0 EGC in each conduit in your hypothetical scenario. Would your proposal change this, or would it clarify this to be the case? If your proposal would change the requirement then I think it needs to make a change to 250.122(F) rather than to (A).

250.122(A) is a more general rule than (F). I think the specific requirement in (F) for the case of parallel conduits trumps the general allowance in (A) that the EGC need not be larger than the circuit conductors.
 
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