grounded neutral conductor requirement for pad mounted w

[jlmott]

I have a situation where a wye/wye transformer is connected with the Ho bushing connected only to the grounding conductor and I am looking for the NEC refrence that specifies the need for a grounded neutral conductor so that the grounding conductor doesn't carry load current. Which article would that be under?jlmott@pplweb.com

[ December 30, 2003, 11:47 AM: Message edited by: jlmott ]

 

[bennie]

Re: grounded neutral conductor requirement for pad mounted w

This is a technical design issue, not a code topic.

The star points of both the primary and secondary are to be solidly connected by the MGN.

 

[roger]

Re: grounded neutral conductor requirement for pad mounted w

Is the XO terminal connected to anything?

For some reason SWER comes to mind but you would know if that were the case.


Roger

 

[bennie]

Re: grounded neutral conductor requirement for pad mounted w

Wye/Wye is often done when the transformers have a single high voltage bushing.

Delta/Wye requires two high voltage bushings.

Pole mounted pots with one HV bushing will have the primary winding internally grounded to the tank. When the neutral tap for the secondary is taken from the tank ground pad the star points are solidly connected.

 

[bennie]

Re: grounded neutral conductor requirement for pad mounted w

JLmott: After more thought, are you sure this is a wye/wye transformer?

 

[dereckbc]

Re: grounded neutral conductor requirement for pad mounted w

wye/wye transformer? What is it being used for. Very rare

 

[bwilson]

Re: grounded neutral conductor requirement for pad mounted w

Wye/Wye is the usual utility trans. in this area. If it is customer owned then you have a problem. In this installation the grounded conductor is regrounded at each location where accessable. This is legal per the NESC but not the NEC. Both X0 and H0 are bonded to a common point in the transformer and inturn are regrounded to a gd. electrode at the vault or pad site.

 

[bennie]

Re: grounded neutral conductor requirement for pad mounted w

bwilson: I read of all the hazards with a floating wye primary and then a grounded wye with equal problems.

I am curious about what is correct, the NEC or NESC?

What do you think?

 

[bwilson]

Re: grounded neutral conductor requirement for pad mounted w

bennie, in my mind both the NEC and NESC approach to grounding are correct. The problems come when you attempt to merge the two systems. By putting a wye/wye transformer in a delta/wye system or the otherway around, delta/wye into a wye/wye system and you use the MV concentrics as both a grounding conductor and as a grounded conductor the danger becomes the fact that the transformer encloser may become energized. Remember that X0 and H0 are bonded together and to the transformer case.
What do you think?