service entrance neutrals

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malachi constant

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Follow up question on a post from a couple months ago. There's no real reason to read through the link, but I figured I will reference it in case someone recognizes the language. http://forums.mikeholt.com/showthread.php?t=191611&highlight=

I have a new question, here is a summary (with updated information):

I have an install going in with a 480V exterior pad-mount delta:wye utility transformer feeding an adjacent connection cabinet. The connection cabinet has no overcurrent protection (which is typical for utility installs in our area). The cabinet will feed some chillers (which have service rated disconnects at them) and also will feed a 480:208V 500kVA delta:wye step down transformer which in turn feeds the building. We added a service entrance rated disconnect ahead of the transformer.

A few questions:
1. Does this installation require a neutral from utility transformer to the primary SE disconnect in front of the stepdown transformer? If so does it need to be full size? It's a weird situation in two ways - (1) we're feeding a transformer more or less straight from a transformer; and (2) in there being a ~service entrance~ disconnect protecting the 2nd transformer. I had a grounding electrode conductor specified from utility to stepdown, but not any neutral. Transformers don't generally require a neutral to them, but does the SE disconnect require one? I'm confused as to what principles take precedence here.
2. Do the chillers also require neutrals from utility xfmr to their SE disconnects? The chillers were specified with grounding electrode conductors but no neutrals.

Thanks in advance!
 
Technically speaking, there is no EGC from the utility service, only a neutral. I'd say yes, that conductor needs to terminate in, and be bonded to, the service disconnect.
 
LarryFine said:
Technically speaking, there is no EGC from the utility service, only a neutral. I'd say yes, that conductor needs to terminate in, and be bonded to, the service disconnect.
Click to expand...

Larry, does it need to have a fully-sized neutral? Could what was specified as an EGC possibly be bonded as the neutral? If a smaller neutral is allowed is there a code that governs that calculation or decision?

The chillers are 571 MCA, with phase conductors of (2) sets of 3-300kcmil+ #1/0.
The stepdown transformer 800A SE disconnect is fed with (3) sets of 3-300kcmil + #2/0.

Considering there is expected to be no significant current on any of the neutrals is there a viable code path to allow smaller neutrals?
 
If you're referring to the grounded conductor or neutral being brought to the service disconnect then it should comply with 230.42(C).

230.42(C) Grounded Conductors. The grounded conductor shall
not be smaller than the minimum size as required by
250.24(C).
Click to expand...
 
infinity said:
If you're referring to the grounded conductor or neutral being brought to the service disconnect then it should comply with 230.42(C).
Click to expand...

Let's see if I follow this...
* 230 Services, Part IV Service Entrance Conductors, 230.42 Minimum Size and Rating, (C) Grounded Conductors shall not be smaller than the minimum size as required by 250.24(C).
* 250.24(C) Grounded Conductor Brought to Service Equipment. Refers to (C)(1) through (C)(4).
* 250.24(C)(2) would apply here - Parallel Conductors in Two More Raceways or Cables. Shall be based on the total circular mil area of parallel ungrounded conductors in the raceway as indicated in 250.24(C)(1), but not smaller than 1/0. 250.24(C)(1) says the grounded conductor shall not be smaller than specified in Table 250.102(C)(1).
* Table 250.102(C)(1), Size of Largest Ungrounded Conductor or Equivalent Area for Parallel Conductors. For the stepdown xfmr 800A disconnect we have (3) sets of 300kcmil, which works out to 900kcmil of conductor, requiring a #2/0 copper grounded conductor, which we have. Similarly for the chillers (2) sets of 300kcmil works out to 600kcmil, requiring a #1/0 grounded conductor, which we have.

So we should be good here, correct? Full size neutral is not required, just need to follow the code path above? I think I did it right, I have just been referring to our conductor as ground, but in fact it should be called a neutral or (technically) a grounded conductor.

Anything I'm missing here? Thanks all!
 
LarryFine said:
I believe that, with no specific neutral current, the conductor can be sized as the EGC that would be required for the supply conductor size/ampacity.
Click to expand...
That is the rule for feeders. For services the grounded conductor can't be any smaller then the minimum required supply side bonding jumper.
 
malachi constant said:
Let's see if I follow this...
* 230 Services, Part IV Service Entrance Conductors, 230.42 Minimum Size and Rating, (C) Grounded Conductors shall not be smaller than the minimum size as required by 250.24(C).
* 250.24(C) Grounded Conductor Brought to Service Equipment. Refers to (C)(1) through (C)(4).
* 250.24(C)(2) would apply here - Parallel Conductors in Two More Raceways or Cables. Shall be based on the total circular mil area of parallel ungrounded conductors in the raceway as indicated in 250.24(C)(1), but not smaller than 1/0. 250.24(C)(1) says the grounded conductor shall not be smaller than specified in Table 250.102(C)(1).
* Table 250.102(C)(1), Size of Largest Ungrounded Conductor or Equivalent Area for Parallel Conductors. For the stepdown xfmr 800A disconnect we have (3) sets of 300kcmil, which works out to 900kcmil of conductor, requiring a #2/0 copper grounded conductor, which we have. Similarly for the chillers (2) sets of 300kcmil works out to 600kcmil, requiring a #1/0 grounded conductor, which we have.

So we should be good here, correct? Full size neutral is not required, just need to follow the code path above? I think I did it right, I have just been referring to our conductor as ground, but in fact it should be called a neutral or (technically) a grounded conductor.

Anything I'm missing here? Thanks all!
Click to expand...
Yes, it is the grounded conductor, which often is also a neutral, but isn't always a neutral.

If the source is grounded, you must run the grounded conductor to the service disconnect and bond it to the GES and from there the EGC continues on. If you don't bring the grounded conductor to the service disconnect you may not have a low enough impedance return path to help with overcurrent protection should there be a ground fault.
 
service conductors bare neutral

service conductors bare neutral

What code cycle made bare neutral service conductor not permitted ?
 
domnic said:
What code cycle made bare neutral service conductor not permitted ?
Click to expand...
Where are you finding any general restriction on using bare conductor for grounded service conductor?

200.6 covers identification of grounded conductors, many of the subsections start off with "An insulated grounded conductor..." If the conductor is not insulated that particular subsection doesn't apply.
 
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