Assist with Concentric Grounding

[eeee]

I have had a dialogue with our tenured chief inspector and would like assitance with this question for his assurance. We have a 100% concentric nuetral XLP primary cable entering a 300KVA, 3 phase, 12,470 volt primary, 120/208Y secondary, delta wye configured transformer. The transformer we are replacing was configured as a wye-wye previously. We are of the belief that since we have a 100% concentric nuetral (and not a 1/3 full concentric nuetral), we do not need a nuetral on the secondary and only need to ground the X0 with a #6AWG, thus using a 3 wire cable and not a 4 wire cable on the secondary. We know to leave the nuetral unconnected on the primary since we are concerting from a wye-wye to a delta-wye and installing a delta-wye pad mounted transformer.

Would you agree?

 

[don_resqcapt19]

Re: Assist with Concentric Grounding

You can't have a 120/208 volt system without a neutral!!!
Don

 

[George Stolz]

Re: Assist with Concentric Grounding

Does 250.20(B) apply to this situation?

 

[bob]

Re: Assist with Concentric Grounding

eeee

We are of the belief that since we have a 100% concentric neutral (and not a 1/3 full concentric neutral), we do not need a neutral on the secondary and only need to ground the X0 with a #6AWG, thus using a 3 wire cable and not a 4 wire cable on the secondary.

The fact that you have a neutral on the primary does not have anything to do with the requirements for a neutral on the secondary. Since you have a delta primary there is no neutral current. The fact that you have a full neutral as opposed to a 1/3 neutral is meaningless. If you did need the neutral, each of the neutrals at 1/3 would be connected together thus giving you a full neutral equal to the capacity of the phase conductors.
AS Don says, you can't get 120 volts on the secondary with out a neutral.
eeee
You definitely need some professional help. You seem to lack the understanding of electrical concepts and its going to get someone in trouble.

[ February 04, 2006, 08:46 AM: Message edited by: bob ]

 

[eee]

Re: Assist with Concentric Grounding

Bob,

This question was for the electrical inspector who I know has a very good understanding of the subject. I must have misunderstood his question that I relayed to you. I plan to call the utility EEs for help for myself when I need teaching in addition to my PE Exam book I must learn from in preparation for my PE.

I lost site that this was a wye connected load and needed a nuetral during my conversations with the electrical inspector. I do have a review department that teaches me, but I get in trouble with them and must learn by myself I have been told and I won't do that on this site out of respect.

I takes me a little time to get up to speed. I have been in telecom for the last 15 years and electronics before that and have not studied power since my BSEE in 1989. I have a MSEE with emphasis on telcom and EE math so I do learn quick and I applogize.

I have been in the power field for 2 years; one of those years was working at the hydro-electric power plants in the northwest. The last year has been in power distribuition.