Equipment grounding conductors for conducors in parallel

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Re: Equipment grounding conductors for conducors in parallel

Hey guys, I need one more opinion on the equipment grounding conductor for the above mentioned feed. 250-118 (1) mentions that copper equipment grounding conductor can be insulated, covered or bare. Any drawbacks to sticking a bare ground in the trench along with the direct buried ABC conductors. How about just putting some 4/0 or 250 THHN directly in the trench as an EGC? This wire is a lot more flexible than most of the bare wire that I have come across, and usually is priced a little bit better.
 
Re: Equipment grounding conductors for conducors in parallel

Originally posted by thunder15j: Regarding the separation issue, one might consider using a triplexed assembly for each of the four runs, then use a 7.5 inch spacing between each run. They are all part of one circuit. Here again, every thing is almost the same as if it were in PVC, except the PVC and of course the full sized equipment grounding conductor in each run.
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What you are saying is that you meet code, except for the areas in which you don?t meet code.

I am not getting through to you, thunder. So I will ask the rest of the Forum for assistance. Am I right, or am I missing something?

I continue to contend that you can NOT NOT NOT NOT do what you are describing. It would be a CODE VIOLATION!!!!!!!!!

To be clear, what I contend is that you must either,
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Install each of the four sets of conductors in conduit,</font>
<font size="2" face="Verdana, Helvetica, sans-serif">OR
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Install all conductors side by side (i.e., in close proximity).</font>
<font size="2" face="Verdana, Helvetica, sans-serif">You do not have the option of separating the conductors within the trench, in an effort to avoid derating, nor in an effort to avoid the cost of the conduits.

I may be wrong about this, and I would welcome comments, but am I at least clear, this time?
 
Re: Equipment grounding conductors for conducors in parallel

Don:

I think I found the answer to your question. 310.7 Direct Burial Conductors:

Cables rated above 2000 volts shall be shielded.

Charlie:

You lost me. Are you saying that even if a ground is ran with each set of parallel conductors, they would still have to group the sets or use conduit? Or does your last post only apply if only one ground conductor is used?

Steve
 
Re: Equipment grounding conductors for conducors in parallel

Steve: What I am saying does not relate to the number of EGCs. You size the EGC on the basis of the overcurrent device. If you have parallel conductors, with each set in a separate conduit, then each conduit must contain a full-sized EGC.

The original post described an installation with four sets of parallel conductors, all in the same trench, and not in conduits. What I am saying is that 300.5(I) requires them to be ?in close proximity.? That tells me that it is not acceptable to run one set (A-B-C-N-G) on one side of the trench, another set 8 inches away, another set another 8 inches away, and the fourth set on the far side of the trench. The original post suggested that this configuration would avoid a derating factor (i.e., for more than 3 current-carrying conductors).

I submit that this would be a violation of 300.5(I). I was hoping to get either an affirmation of, or a contradiction to, my views.
 
Re: Equipment grounding conductors for conducors in parallel

Charlie, I am wondering what is the safety hazard that would arise from the conductors being laid out like you described? I think it might be for the same reason as why one needs to install a full sized EGC in each conduit when installed in a ductbank in a trench. Even if there is a full sized EGC installed with each group of cables and laid out as you described, I can still maybe see some danger in someone later on working in that area and digging up the ground and finding only some of the cables that are buried and assuming they found all of the cables and then hit the other cables inadvertantly :eek: . There could also be some other reason not to do this as well that I haven't thought of. Also, the wording "in close proximity" in 300.5(I) is vague, but IMO the intent of the section is as you have interpreted.
 
Re: Equipment grounding conductors for conducors in parallel

Charlie:

It seems to me that Exception #1 (300.5I) is allowing each group to be separated where each group includes all the phase conductors and a ground. It looks like 300.3(B) (1) may also be allowing this:

The requirement to run all circuit conductors within the same raceway,....trench....shall apply separately to each portion of the paralleled installation.
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Just my opinion. Of course, none of this applies if there isn't a ground for each "group" of conductors.

Steve
 
Re: Equipment grounding conductors for conducors in parallel

Steve: Exception 1 to 300.5(I) does not apply here. It talks about conductors in raceway or cable. This discussion is about individual conductors (i.e., not in "cable") installed in a trench (i.e., not in raceway).

David: I think you have a good reason (if not actually the original reason) for this requirement. If the conductors are not "in close proximity," then you won't find them all when you dig.
 
Re: Equipment grounding conductors for conducors in parallel

Originally posted by steve66:It looks like 300.3(B) (1) may also be allowing this
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That is possible; digging four parallel trenches, and laying a complete set of A, B, C, N, and (full-sized) G in each trench, appears to satisfy this article. But here again it is not the same as the configuration proposed in the original question. ?Thunder15j? wants to dig a single trench, and use some convenient method to separate each set of A-B-C-N-G. I don?t think that 300.3(B)(1) would not allow that method.
 
Re: Equipment grounding conductors for conducors in parallel

Charlie:

If it is Ok to lay them is separate trenches, wouldn't you agree that spacing them in a single trench would also be OK? To me the end result seems to be the same. And one seems to be just a safe as the other.

Steve
 
Re: Equipment grounding conductors for conducors in parallel

I agree with Steve, IMO 300.5(I) is implying all conductors of the same circuit to mean that in a parallel installation, all parallel runs consitute the circuit, in which case all cables would need to be in the same trench.
 
Re: Equipment grounding conductors for conducors in parallel

Originally posted by steve66: If it is Ok to lay them is separate trenches, wouldn't you agree that spacing them in a single trench would also be OK? To me the end result seems to be the same. And one seems to be just a safe as the other.
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I figured you would pick up on that anomaly. So did I. To be clear, lets consider the following two situations:
</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Dig one wide trench. Put in some type of racks or spacers, so that you could lay out four separate sets of A-B-C-N-G, and can keep them perhaps 8 inches apart. Then fill in the trench with dirt. The dirt between the spacers creates an effective barrier between the four sets of conductors.</font>
<font size="2" face="Verdana, Helvetica, sans-serif"></font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">Dig four side-by-side narrow trenches. Put a set of A-B-C-N-G in each. Fill in each trench with dirt.</font>
<font size="2" face="Verdana, Helvetica, sans-serif">I can?t give you a clear technical reason why the two are different. If I were an Inspector, I might accept the two as being equivalent. But as the code is presently written, the first is not allowed, and the second is allowed. So perhaps it would be necessary to clear the proposal with the AHJ.

I will say, however, that I would not accept a single, wide trench, unless there were a means to provide, and maintain, physical separation between the four sets of conductors. If they were simply laid on the ground, there is no way to make sure that one or more wires from one set would not be pushed close to another set during the backfilling process.

I think the best solution is to use conduit. That meets the letter of the code, and raises no questions.
 
Re: Equipment grounding conductors for conducors in parallel

Charlie:

That sounds reasonable, and I don't think I can take issue with anything you said. I think I would allow one trench also, if I were the inspector.

Thankfully, I'm not an inspector :) I get the luxury of debating this without having to actually make a tough call on what is or isn't allowed.

Steve
 
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