Primary side bonding

[JdoubleU]

I have a question on how this system might be bonded so it trips an overcurrent device in case of a ground fault. The system is a 480v, 3 phase delta to 208v y. The y makes since, the center tap and neutral is bonded to the equipment ground thus creating a low resistance path to trip the overcurrent device. If 480 is brought to the building and has no neutral and is only operating some hvac equipment, How is it typically bonded so that if there is ever a ground fault it provides a low resistance path to trip the overcurrent device.

 

[petersonra]

I have a question on how this system might be bonded so it trips an overcurrent device in case of a ground fault. The system is a 480v, 3 phase delta to 208v y. The y makes since, the center tap and neutral is bonded to the equipment ground thus creating a low resistance path to trip the overcurrent device. If 480 is brought to the building and has no neutral and is only operating some hvac equipment, How is it typically bonded so that if there is ever a ground fault it provides a low resistance path to trip the overcurrent device.

unless it is corner grounded or midpoint grounded delta a ground fault won't trip the overcurrent device.

 

[BPoindexter]

Is the supply system itself Delta? It sounds like you may be referring to the Primary of the step down transformer where Delta/Wye is ceratinaly the most common used.

 

[JdoubleU]

Yes

 

[BPoindexter]

Well just as Mr Bob said then. If ungrounded it should have a Ground Detection system installed. They are required now but used to be just "recommended" so if it is an older system may not have one.

 

[iceworm]

I have a question on how this system might be bonded so it trips an overcurrent device in case of a ground fault. The system is a 480v, 3 phase delta to 208v y.

... If 480 is brought to the building and has no neutral and is only operating some hvac equipment, How is it typically bonded so that if there is ever a ground fault it provides a low resistance path to trip the overcurrent device.

Assumption:
Op is concerned with tripping the transformer primary feeder in the event of a ground fault in the feeder conductors or a ground fault the xfm primary winding

Jake -
First you must know the type of 480V system supplying the feeder. Yes I understand the xfm primary is delta and the primary feeder is 3W, 480V 3ph. That does not adequately describe the feeder system.

Probable systems (in order of likely hood):
480Y solidly grounded
480Y impedance grounded
480D corner grounded
480D corner grounded
480D, midpoint grounded (highly unlikely - but possible, right up there with getting hit by a meteor)

Second:
Is there a EGC in with the feeder conductors?
Is the feeder conduit metalic and continuous?
Is there a ground grid, or other low impedance connection between buildings?

Know these two and you will have the answer.

ice