EGC Sizing Question

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R0bG

Member
Hello,

I have a question regarding EGC sizing on a project that I'm currently working on. There is some verbiage in the hand book that is confusing to me that I was hoping that one of you guys could help clarify it for me.

Here is the situation in the field.

- A 2000A breaker feeds a load that sits about 150' away. The 2000A breaker is set to trip at 1800A.
- Between the breaker and the load there are (5) 3/c 500kcmil XHHW-2 cables that are routed on a cable tray all the way to the load.
- The 3/c 500kcmil XHHW-2 cables have a #2 ground built into the cable.

My understanding is that the ECG should be sized at 250kcmil based on T250.122.

I'm pretty sure that the EGC should be 250kcmil but just wanted to double check with you guys just in case there is an exception somewhere that I may not be aware of.

Thanks!
 

jumper

Senior Member
I get a 250kcmil EGC also, based on the full rating of the breaker @ 2000A.

This problem crops up when trying to parallel conductors using cables, often the cable will have an undersized EGC for this application.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
You have it correct. This is a common problem with using parallel multi-conductor cables. The standard versions do not have a large enough EGC, and to get it large enough requires a special order from the manufacturer ($$$$). That is a big reason I always use single conductors for parallel installations.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
No fair, Jumper! I was typing my answer when I was interrupted by a co-worker with a question. :(
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
I have a project going that has the same situation in numerous feeders so we have done as Charlie does, we changed all the parallel tray cable to single conductors.

Roger
 

ron

Senior Member
As well as the #2AWG EGC is too small to be paralleled. 310.4(H) says 1/0 or larger, although a smaller EGC in a cable is ok per 310.4(H)(5), if it complies with T250.122, which the #2 doesn't.

Maybe you can cut the #2 is it emerges from the cable jacket on each end, and run a single full sized EGC on the tray.
 

Smart $

Esteemed Member
Location
Ohio
...Maybe you can cut the #2 is it emerges from the cable jacket on each end, and run a single full sized EGC on the tray.
I am pretty sure The EGC needs to be in the cable and not run separate.
I agree... I see it as a 300.3(B) issue and do not see anything in 250.122(F) that changes my mind.
Don and I have went round 'n' round about this before. While I respect his opinion (as his opinion :D), I disagree with it for a cable tray installation, where there is no other wiring method used at any point in the run.

Consider that 300.3(B)(2 specifically says parallel installation runs in cable tray...
(1) Paralleled Installations. Conductors shall be permitted
to be run in parallel in accordance with the provisions of
310.10(H). The requirement to run all circuit conductors
within the same raceway, auxiliary gutter, cable tray, trench,
cable, or cord shall apply separately to each portion of the
paralleled installation, and the equipment grounding conductors
shall comply with the provisions of 250.122. Parallel runs
in cable tray shall comply with the provisions of 392.20(C).

392.20...
(C) Connected in Parallel. Where single conductor cables
comprising each phase, neutral, or grounded conductor of
an alternating-current circuit are connected in parallel as
permitted in 310.10(H), the conductors shall be installed in
groups consisting of not more than one conductor per phase,
neutral, or grounded conductor to prevent current imbalance in
the paralleled conductors due to inductive reactance.

Single conductors shall be securely bound in circuit
groups to prevent excessive movement due to fault-current
magnetic forces unless single conductors are cabled together,
such as triplexed assemblies
.

My conclusion: a single EGC is permitted... but you can't use the combined cable EGC cmils to qualify as such... and again I reiterate that there can be no other wiring method used in the run.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Don and I have went round 'n' round about this before. While I respect his opinion (as his opinion :D), I disagree with it for a cable tray installation, where there is no other wiring method used at any point in the run.

Consider that 300.3(B)(2 specifically says parallel installation runs in cable tray...


392.20...


My conclusion: a single EGC is permitted... but you can't use the combined cable EGC cmils to qualify as such... and again I reiterate that there can be no other wiring method used in the run.
Yes, we have, and my opinion stands....as long as you are using a "cable" the EGC must be a part of that cable no matter where the cable is installed. I see nothing in your citations that changes my opinion.

We just read the same words differently. I would cite the same sections to support my opinion.
 

ADub

Senior Member
Location
Midwest
Occupation
Estimator/Project Manager
As well as the #2AWG EGC is too small to be paralleled. 310.4(H) says 1/0 or larger, although a smaller EGC in a cable is ok per 310.4(H)(5), if it complies with T250.122, which the #2 doesn't.

Maybe you can cut the #2 is it emerges from the cable jacket on each end, and run a single full sized EGC on the tray.

I've had this argument at work before. Are equipment grounds permitted to be paralleled at less than 1/0 if they are complying with 250.122 and ran full size in each raceway? I know a guy that claims this is the case and that we are also allowed to reduce the grounded conductor to the egc size if it is enough to carry the neutral load. So for example a parallel run for a 400 amp machine would have 2 conduits with three 3/0s and two #3s in each. I think it's completely non compliant but I've seen it pass here.


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Smart $

Esteemed Member
Location
Ohio
I've had this argument at work before. Are equipment grounds permitted to be paralleled at less than 1/0 if they are complying with 250.122 and ran full size in each raceway? I know a guy that claims this is the case and that we are also allowed to reduce the grounded conductor to the egc size if it is enough to carry the neutral load. So for example a parallel run for a 400 amp machine would have 2 conduits with three 3/0s and two #3s in each. I think it's completely non compliant but I've seen it pass here.
Parallel EGC's are not subject to the 1/0 and larger stipulation of 310.10(H)(1).

Neutral conductors are only required to be sized for the calculated maximum unbalanced circuit current, for circuits not subject to small conductor rules of 240.4(D), but not smaller than the required equipment grounding conductor.
 

ADub

Senior Member
Location
Midwest
Occupation
Estimator/Project Manager
Parallel EGC's are not subject to the 1/0 and larger stipulation of 310.10(H)(1).

Neutral conductors are only required to be sized for the calculated maximum unbalanced circuit current, for circuits not subject to small conductor rules of 240.4(D), but not smaller than the required equipment grounding conductor.

So to put it plainly- are neutral conductors allowed to be run in parallel in sizes smaller than 1/0 even if the unbalanced current is smaller than a 1/0 capacity?


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Smart $

Esteemed Member
Location
Ohio
So to put it plainly- are neutral conductors allowed to be run in parallel in sizes smaller than 1/0 even if the unbalanced current is smaller than a 1/0 capacity?
No. Parallel neutral conductors are subject to the stipulations of 310.10(H)(1). It is only EGC's that are not.

I see I failed to iterate that in my earlier reply. :ashamed:
 

ADub

Senior Member
Location
Midwest
Occupation
Estimator/Project Manager
No. Parallel neutral conductors are subject to the stipulations of 310.10(H)(1). It is only EGC's that are not.

I see I failed to iterate that in my earlier reply. :ashamed:

Thanks. This was my stance as well. I was given 215.2(a)(2) as a substantiation but the way I see it 215.2(a)(2) is the section that forbids it


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