Ray Cyr

A Commercial/Industrial application, 240/120v "320" service, parallel 250mcm ungrounded conductors per phase from the point of service (overhead) down through the single mast to the meter base.
We ran a single 3/0 for the grounded conductor in this mast (we happened to have some 3/0 on hand) and figured we were done with it. The inspector said that if we had ran a grounded conductor that was no more than 2 sizes smaller (350mcm) than the ungrounded conductors (500mcm equivilent) he would have passed it without question, but since we ran 3/0 we needed to parallel this also, since the ungrounded were ran in parallel. He searched for a code reference but could not find what he was looking for. We told him we oversized according to 250.66 (minimum being 1/0) and it only had to be one conductor per 250.24(C)(2).

What are your thoughts on this?
Thanx,
Ray

480sparky

310.4(B) maybe?

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All responses based on the 2008 National Rat Code.

Ray Cyr

We thought that might be what he was looking for but that only applies to when you have to use parallel conductors and we don't see the need to run parallel for the grounded in this situation.

480sparky

310.4(B) states the neutral is included in this shopping list of requirements. 310.4(B)(3) says they all must be the same size in cmil area. Maybe the inspector is interpreting this as saying you need a full-size (and paralleled) noodle.

__________________
All responses based on the 2008 National Rat Code.

Ray Cyr

Ah, I see what you are saying and how this could be interpreted that way. Thank you for pointing that out .
With this in mind, what is your opinion? Does this conflict with 250.66 and 250.24 (C)(2)? Or does it supplement it? If it does conflict, which article should take precedent for a grounded conductor?

Ray Cyr

Does anyone else have any thoughts on this? If I am wrong here I really would like to know

480sparky

Your inspector should know that if he can't supply a valid Code reference, then your install should be passed.

__________________
All responses based on the 2008 National Rat Code.

rewire

310.15 b (4)

Magnettica

After reading 250.24 (C)(2), my interpretation is that the grounded neutral conductor needs to be the same size (in kcmils) as the phase conductors. I haven't done the math or checked the kcmil comparison yet though.

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classicelectriconline.com

wareagle

250.24(C)(2) requires that the phase conductors in parallel be the same size and characteristics. The neutral is not included. 250.24(C)(1) requires the neutral be sized not smaller than shown in 250.66 with max being 3/0. Your inspector does not have a code reference to stand on.

electures

(1) Routing and Sizing. This conductor shall be routed with the phase conductors and shall not be smaller than the required grounding electrode conductor specified in Table 250.66 but shall not be required to be larger than the largest ungrounded service-entrance phase conductor. In addition, for service-entrance phase conductors larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded conductor shall not be smaller than 12½ percent of the area of the largest service-entrance phase conductor. The grounded conductor of a 3-phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors. See related ROP

(2) Parallel Conductors. Where the service-entrance phase conductors are installed in parallel, the size of the grounded conductor shall be based on the total circular mil area of the parallel conductors as indicated in this section. Where installed in two or more raceways, the size of the grounded conductor in each raceway shall be based on the size of the ungrounded service-entrance conductor in the raceway but not smaller than 1/0 AWG.

I don't see a problem with your installation. I do, however, have a problem with the inspectors statement about sizing it two sizes smaller. Once again this old wives tale about two sizes smaller appears.

Rather than re-type everything, please read my posts at the end of this thread (disregarding the third grade comments from other posters);

neutral size rule

Good luck!

Ray Cyr

Thank you to all for your responses, I truly appreciate your time and ability to bring so much expertise to the discussion! One of the few trades where someone can learn new things and get new understandings almost everyday, gotta love it