Equipment grounding conductor with secondary

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mistermudd

mistermudd

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Washington State
I recently looked at an installation of a portable at a school. This particular job is really bugging me because after much time and research I have not been able to answer a question to my satisfaction. Three phase 480 volt with equipment grounding conductor in non-metallic raceway ran from an existing panel in the school to an OUTSIDE transformer. Equipment grounding conductor is bonded to transformer frame. Secondary is 208/120 volt; three ungrounded conductors & the grounded conductor with NO equipment grounding conductor; again non-metallic raceway to a 200 amp panel in the portable. The secondary conductors are located outside until they enter the back of the panel. Panel at portable is bonded with main bonding jumper and a grounding electrode system was installed (just like a new service).
Here is my problem. Is the equipment grounding conductor required with the secondary conductors? A short circuit at the portable would not be cleared by the primary overcurrent protection but the secondary conductors are protected by the 200 amp breaker where they terminate at the portable. Another issue I have is the fact that there are low voltage system installed between the school and new portable. In my opinion there is a difference in potential between the low voltage systems ground and the new line voltage ground established at the portable. There is not a complete line voltage equipment ground from the school to the portable.
Is it a code violation NOT to have the equipment grounding conductor ran with secondary? Would another solution be to bond the grounded conductor(x0) again at the transformer, using the grounded conductor also as the equipment ground? This seems to be a situation where this would be compliant with the code. Thanks for any help.
 
mistermudd said:
Secondary is 208/120 volt; three ungrounded conductors & the grounded conductor with NO equipment grounding conductor; again non-metallic raceway to a 200 amp panel in the portable.
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Assuming the grounded conductor is bonded to both the transformer frame and the panel it sounds like it may be code compliant under 250.30(A)(1) Exception No. 2
 
The low voltage system should be bonded to the GEs at both the main building and the portable. This, IMO, makes this instalation require an EGC.


edit to add: "Low voltage system" isn't specific. I'm assuming (yes, I know) that this is a communication system. 800.100 requires the bonding, and 250.32(B)(2) doesn't allow a continuous metallic path between structures when using the neutral as the fault path
 
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JohnJ0906 said:
The low voltage system should be bonded to the GEs at both the main building and the portable. This, IMO, makes this instalation require an EGC.
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John, That can be legally accomplished without the EGC.
 
JohnJ0906 said:
I think it is the transformer that is throwing me off. I only see situations like this with a straight-up feeder.
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John, many things are complicating this to me.

The transformer and 250.30

The Feeder or transformer tap and 250.32

Then there is a question in my mind about the suitability of these 'portables' to be supplied using the neutral as the grounding means. More of a listing issue then a NEC issue.

If I was wiring it I would have run a EGC just to keep things easy with no questions. :smile:
 
JohnJ0906 said:
Installing an EGC - $100
Applying the KISS principle - Priceless!

:D
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Exactly....:grin:

Here at the forum I have time to debate the details, at the job I want the inspector in and out with nothing to ask or worry about.
 
Thanks for all the quick responses. I am an inspector and this is a job I looked at. My first impression was that the secondary was just like a new service and the installation was okay. Since it is a public school I started having second thoughts. Some of the points & questions you brought up are:

1) The grounded conductor is NOT bonded at the transformer. Terminates on X0 with no bond to frame at transformer. If this bond was installed per 250.30(A)(1) ex 2 would the low voltage systems establish a parallel path voilating this section? Or would the parallel path be metallic raceway with the secondary conductors?

2) There is water but I am not sure if it is metal water pipe between buildings. I don't think this makes much of a difference because of the low voltage systems (ie fire alarm, intercom & data) already provide another ground path from building to the portable.

3) The listing of the portable may be a valid point but as I rememeber the panel was setup as service. It seems like all that needed to be done was install the provided main bond screw. I could be wrong about this because many buildings of this type are setup to fed by a feeder.

4) I have went thru Soares 8th edtion chapter 12 about 10 times and it shows just about every possible configuration. Including figure 12-9 which is single phase but shows how this is system is grounded and bonded.

I agree 100% with the statement that if the EGC was installed it would be a done deal but it is not.
Adding a transformer into the mix certainly made this a more complex issue. It is not a straight up feeder between two buildings.

So is this a violation or not and if so what section did they violate?

Thanks for any help and/or input.
 
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