Grounding at a service trough

[brian john]

I looked at a service today that utilizes a 12X12 trough, the neutral is mounted to the back box and grounded per the NEC, in the trough. There are 3 MCB panels each is fed from the trough with a PVC nipple, each PVC nipple has 3 phase conductors and a neutral, in the panel the neutral bonded per NEC.

Should there be separate grounding conductor in the PVC nipple?

 

[Paul M]

I think a separte ground to the trough would create a parrallel path, not a good thing unless the ground was the same size as the neutral.

 

[brian john]

Paul:

While you are correct, this situation, parallel paths are set up at services all the time with this type on installation. If the nipples were metallic the neutral is still required to be bonded in the service disconnect and in the trough.....Parallel paths.

 

[bphgravity]

No, EGC's aren't required and will not serve any purpose until after the first disconnecting means. All fault current and normally operating current uses the grounded service conductor on the supply side of the main disconnecting means.

 

[George Stolz]

Brian John, check out 250.92(B)(1).

 

[electrofelon]

Brian John parallel paths are set up at services all the time with this type on installation

It seems that the code gives conflicting information. 250.92(B)(1) states ok to bond service raceways with the neutral, and as brian john said, this offen creates parallel paths when one uses metallic nipples. But then there is the section on parallel paths (cant find it at the moment but i know its there!). So couldnt one argue that in certain situations, you would have to keep the neutral isolated from a raceway/j-box and bond that raceway/j-box by other means, i.e 250.92(B)(2-4)?

 

[bphgravity]

The code does state that objectionable currents created by grounding (service supply side bonding) methods should be prevented, however it doesn't tell us what objectionable is exactly or what the quantifiable value of objectionable current is.

 

[electrofelon]

Where is that section on parallel paths? I just looked at 250.6 but I remember a section that used the phrase something like "a parallel path shall not be created......" I remember it because I got cited for it once
Is there such a section or maybe thats what the inspector wrote down using 25.6 as the basis?

 

[bphgravity]

Your probably thinking of 250.24(A)(5) ?

 

[brian john]

I would like to thank everyone for their responses.

 

[electrofelon]

I thought there was a code article that specifically stated that a parallel path shall not be created, hence my thoughts that the code offered conflicting information. I cant find it and apparenty no one else can so perhaps that phrase was just the inspector's own words. Anyone with an electronic version want to do a search for "parallel path"?

 

[don_resqcapt19]

The only place the pharse "parallel path" appears in the NEC is in 250.30(A)(1)Ex #2

 

[electrofelon]

Thanks Don,

Yeah that would not have applied, must have been the indpectors own words based on 250.6 I am recalling.