Grounding transformer to enclosure

[cuky2000]

A manufacturer of 345 kV circuit breaker provided a 7.5 kVA transformer 480-240/120V for with a neutral grounded on the control cabinet. This cabinet is bolted to the metallic part of the circuit breaker witch is grounded to the substation ground grid at the base.

The local utility engineer is challenging the transformer grounding to the enclosure instead a direct grounding conductor connected to the substation ground grid.

I have a hard time finding any code violation or no compliance to the NEC, IEEE, NESC etc. regarding the grounding proposed by the manufacturer.

Please advise if there is any objectionable grounding in this arrangement.

Thanks

 

[NAZ55]

I think this is what you are after.

http://www.mikeholt.com/reprint_request2000.php?id=4394

I don't see a problem with this.

 

[NAZ55]

This material was extracted from Mike Holt Training Materials copyright 2007 by permission. Visit

http://www.MikeHolt.com

or call 1.888.NEC.CODE (632-2633) for more information.

 

[cuky2000]

Thanks Zazmat

 

[dpc]

cuky,

I think the concern may be the reliability over time of using the enclosure as a ground path, especially on a high voltage breaker. As corrosion sets in, the ground path through the bolts and metal-to-metal interfaces could increase in resistance.

I do not think it is an NEC issue, but just question of what is the "best practice".

 

[jghrist]

I assume that the transformer is for local auxiliary power purposes. If this is the case, then no load or fault current on the secondary will flow through the ground grid anyway. There is no question of reliability of the path to the ground grid since it will never carry any current.