Equipment Grounding Conductor Size

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mfranklin

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I'm currently working on a project where we have a 4000A incoming service with 13 parallel runs of 4-500MCM AL and 1-500MCM AL equipment ground. The inspector is stating per Table 250.122 that equipment ground must be a 750MCM AL. The engineer of record and us are saying that per 250.122(A) the equipment grounding conductor does not have to be larger than the circuit conductors supplying the equipment. Thoughts?
 
Please clarify your question. You are using conflicting terms. If this really is a "service," one that is fed from the serving utility via a service transformer, then there would not be an EGC (or any other conductor whose name includes the word "ground") run with the service conductors.
 
This service entrance feeder is on the secondary side of the Utility transformer. It is fed with 13 parallel runs of 3-500MCM AL ungrounded conductors, 1 - 500MCM AL Neutral and 1 - 500MCM AL Equipment Grounding conductor.
 
There is no such thing as an "Equipment Grounding Conductor" until you are at, or are downstream of, the location of the first disconnecting means on the secondary side of the transformer. This is most often in the main service switchboard, and is also where the N-G bond is located. Based on your description, my response is to suggest removing the wire you are calling an EGC. It is not required, and it would serve no purpose.

Oh, I forgot to add to my original post, "welcome to the forum."
 
mfranklin said:
This service entrance feeder is on the secondary side of the Utility transformer. It is fed with 13 parallel runs of 3-500MCM AL ungrounded conductors, 1 - 500MCM AL Neutral and 1 - 500MCM AL Equipment Grounding conductor.
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Service entrance means 3 ungrounded and one grounded conductor. Is there a disconnect on the load side of the transformer at the unit? If not then no equipment grounding conductor is required.
 
mfranklin said:
I'm currently working on a project where we have a 4000A incoming service with 13 parallel runs of 4-500MCM AL and 1-500MCM AL equipment ground. The inspector is stating per Table 250.122 that equipment ground must be a 750MCM AL. The engineer of record and us are saying that per 250.122(A) the equipment grounding conductor does not have to be larger than the circuit conductors supplying the equipment. Thoughts?
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Both the inspector and engineer are incorrect. As Charlie stated you will not have any EGC's on the line side of the service disconnect, all metallic parts and racewaysare bonded to the neutral.
 
Thanks for the welcome and quick replies. I've been using the forum for sometime but this is my first post. A lot of great info and a great resource.

I apologize I should have explained further, this is from a Secondary Connection Cabinet where the N & G are bonded to the main switch gear.
 
So, if it's a feeder, and you have metallic conduits, still remove the EGC.

If it's non-metallic, each EGC must be sized as if it were the only one.
 
mfranklin said:
. . . this is from a Secondary Connection Cabinet where the N & G are bonded to the main switch gear.
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Sorry, but your description continues to confuse me. I don't know what you mean by "Secondary Connection Cabinet." My questions:
1. Starting at the transformer secondary terminations, where is the first overcurrent device?
A. Is it the main breaker in the service switchgear?​
B. Is it internal to the "Secondary Connection Cabinet"?​
C. Is it somewhere else?​

2. Where is the N-G bond made?
A. Is it internal to the service switchgear?
B. Is it internal to the "Secondary Connection Cabinet"?
C. Is it somewhere else?

​
3. What do you mean by saying, "where the N & G are bonded to the main switch gear"?

Regarding question 1, the conductors from the transformer secondary terminations to the location of the first overcurrent device will not include any manner of ground wire.
Regarding question 2, every circuit downstream of that point will require an EGC.
Regarding question 3, for every type of panel, including switchgear, switchboard, distribution panel, branch panel, and motor control center, the ground bus that is internal to the panel will be bonded to the panel's exterior enclosure. But only at one location will the neutral bus internal to a panel be bonded to the ground bus of the same panel. That happens only at the answer to question 2 (which, by the way should be the same answer for question 1).
 
Let me try rephrasing, we have a feeder that is 4000A, 13 - parallel runs of 5 - 500MCMs AL (3-phase conductors, 1-neutral and 1-equipment ground). This is a feeder and in PVC conduit underground.
The question is for sizing the equipment ground, the NEC tells us to use Table 250.122 which states for a 4000A over current device use a 750MCM AL. However, article 250.122(A) states "Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment......"

So based on 250.122(A) the equipment ground should be sized no larger then the phase conductors which is a 500MCM. The engineer for the project designed it as a 500MCM and the inspector thinks it should be a 750MCM.
 
I am soooo confused--

"What we have here is a failure to communicate"--​
Please give us a drawing--It appears we have a terminology conflict here--
 
mfranklin said:
Let me try rephrasing, we have a feeder that is 4000A, 13 - parallel runs of 5 - 500MCMs AL (3-phase conductors, 1-neutral and 1-equipment ground). This is a feeder and in PVC conduit underground.
The question is for sizing the equipment ground, the NEC tells us to use Table 250.122 which states for a 4000A over current device use a 750MCM AL. However, article 250.122(A) states "Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment......"

So based on 250.122(A) the equipment ground should be sized no larger then the phase conductors which is a 500MCM. The engineer for the project designed it as a 500MCM and the inspector thinks it should be a 750MCM.
Click to expand...

The circuit conductor size in this case is the total of all 13 sets of 500 kcmil (6500 kcmil) so a 750 EGC is required in each raceway and it is not larger than 6500 kcmil.
 
mfranklin said:
This service entrance feeder is on the secondary side of the Utility transformer.
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mfranklin said:
Let me try rephrasing, we have a feeder that is 4000A. . . . This is a feeder and in PVC conduit underground.
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I don't think you understand why you are confusing us. You are using the two words "service" and "feeder" incorrectly, and it makes all the difference in the world.
  • "Service conductors" originate at the secondary terminals of the "service transformer," and that component is most often owned by the utility company.
  • "Feeder conductors" originate at the "main service panel" or at any other panel downstream, and terminate at another panel.
  • Your first statement quoted above incorrectly used both the words "service" and "feeder." A conductor can serve one of those purposes, but not both.
  • Your first statement that I quote above says that the conductors originate at the transformer. That would make them "service conductors."
  • Your second statement that I quote above calls twice calls the conductors under discussion a "feeder."

So let me rephrase an earlier question. What exactly is a "Secondary Connection Cabinet," does it include an overcurrent device, is it installed between the transformer and the main service panel, and is the N-G bond located internal to that cabinet?
 
mfranklin said:
The question is for sizing the equipment ground, the NEC tells us to use Table 250.122 which states for a 4000A over current device use a 750MCM AL. However, article 250.122(A) states "Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment......"
Click to expand...
That refers to single conductor sets, not multiple sets.
 
Other members of the Forum cleared up this type question for me.
IF we are talking about a feeder (a circuit protected at its source by an overcurrent device) then 250.122(F) {17 Code} will require each conduit have a 750 kcmil AL equipment grounding conductor.
 
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