Neutral Conductor

[brett.knutson]

I am currently serving in Afghanistan with the US Army Corps of Engineers. On site here we have a bunch of 3 conductor, 4/0, direct bury cable. All of our distribution is done 3 phase, 4 wire.

Is there any kind of stipulation in the code preventing the use of this 3 conductor cable with a seperate 4/0 single conductor for the neutral, and a bare #6 for ground?? If so, can you provide the reference in the NEC??

Most of the loads are fairly linear, harmonics are of little concern. Let me know what you guys think.

 

[jeff43222]

Re: Neutral Conductor

I think you're OK as long as the neutral and ground are kept with the phase conductors. 300.5(I) says they must be in the same cable, raceway, or close proximity in the same trench.

Off the top of my head, #6 seems a little small for a grounding conductor if the phase conductors are 4/0. Table 250.66 says you'll need #4 copper if the 4/0 conductors are aluminum, and #2 copper if the phase conductors are copper.

 

[brett.knutson]

Re: Neutral Conductor

Thanks for the prompt feedback. You are right, we do use #2 CU for ground, fat fingered it there

 

[don_resqcapt19]

Re: Neutral Conductor

Actually 300.3(B) and the previously cited section prohibit that installation. Both code sections require that where a cable is used, all conductors of the circuit must be in the cable.
Don

 

[marinesgt0411]

Re: Neutral Conductor

when I was in the Marine Corps and had to wire the generators to the base camps with three wire cable I connected three cables to the generator L1 LO and ground one cable L2 LO and ground second cable L3 LO ground for third cable that way I could split the camp into three sections and more closely balance the load officers had a tendency to overload the circuits with hot plates and coffee pots

 

[rich000]

Re: Neutral Conductor

I am curious, don't you have some sort of manual that tells you what to use? From what I remember being in the Navy, installations did not always comply with the NEC (whether on sea or shore). But there was always some tech manual around telling you exactly how to do an installation or maintenance.

 

[brett.knutson]

Re: Neutral Conductor

Thanks for all the feedback guys. We use Square-D I-Line 400A and QO 225A 3-phase load centers for all of our installations, this ensures the load is balanced. All of our installations must comply with the NEC, regardless of the half assed military manuals out there.

As per the NEC, I assume this 3 conductor cable can only be used for a 240v 3 wire or a 3 phase delta system, neither of which we use here at all (low voltage anyway. I do have some 13.8kV delta however). What a waste of cable, are any of you familiar with KBR?? Your tax dollars hard at work.

[ October 04, 2005, 01:03 PM: Message edited by: brett.knutson ]

 

[don_resqcapt19]

Re: Neutral Conductor

brett,

As per the NEC, I assume this 3 conductor cable can only be used for a 240v 3 wire or a 3 phase delta system,

If the cable does not have an EGC, then it can't be used for those purposes either.
Don

 

[al hildenbrand]

Re: Neutral Conductor

brett.knutson

Does the 3 conductor, 4/0, direct bury cable you are asking about have a metallic covering?

2005 NEC 300.5 Underground Installations
(I) Conductors of the Same Circuit All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors shall be installed in the same raceway or cable or shall be installed in close proximity in the same trench.

The way I read this, if the conductors are in the same trench and in close proximity and 300.3(B)(3) is satisfied, then it doesn't matter if individual conductors run along with the cable.

Edit to complete Code ref # - Al

[ October 04, 2005, 03:18 PM: Message edited by: al hildenbrand ]

 

[brett.knutson]

Re: Neutral Conductor

It has a bare grounding conductor, no metallic sheathing. I am getting conflicting reports out of the NEC:

300.3(B) states "shall be contained within the same cable or cord" I assume this is for interior wiring?

300.5(I) states "shall be installed in close proximity in the same trench" This is my situation, direct burial.

Thanks,
Brett

 

[don_resqcapt19]

Re: Neutral Conductor

Al,
I don't read it that way. In my opinion there are three different choices and they cannot be used in combination. You can use a raceway or a cable or individual conductors installed in close proximity.
Don

 

[al hildenbrand]

Re: Neutral Conductor

Don,

The difference between "cable" and "direct bury conductor" is what this all hinges on. While I want to get into a discussion about isolated phase installations, it will probably help Brett the most to check out the 3C 4/0 for any labeling.

Brett.Knutson,

A little investigation of that 3C 4/0 that you have on the spool is probably in order. The fact that you note it not having any covering is important. I wonder is it is really a cable, as you called it in your opening post. I'll just bet you've got "direct bury conductors" put up in a triplex wrap.

What's the information on the conductors?

Just had to correct my posting - Al

[ October 05, 2005, 01:58 PM: Message edited by: al hildenbrand ]