UNgrounded System

[augie47]

Customer wants a 480 volt ungrounded system.
The only pad transformers POCO has are 480Y/277. To satisfy the customers request POCO elects no leave XO at the pad totally disconnected (no bond strap, no ground rod).
Any problem ?

 

[iwire]

I believe it is fine and I think Charlie E the utility guy mentioned that was something the POCO he works for does it.

 

[K8MHZ]

Customer wants a 480 volt ungrounded system.
The only pad transformers POCO has are 480Y/277. To satisfy the customers request POCO elects no leave XO at the pad totally disconnected (no bond strap, no ground rod).
Any problem ?

As I read 250.20 (B) (1) through (3), no.

This is worth pursuing beyond one section, though.

Anyone with precedence willing to chime in??

 

[Volta]

Customer wants a 480 volt ungrounded system.
The only pad transformers POCO has are 480Y/277. To satisfy the customers request POCO elects no leave XO at the pad totally disconnected (no bond strap, no ground rod).
Any problem ?

And no neutral conductor in the lateral, right? No need for 277v?

Is it large enough to think of 230.95 GFP?

Probably not our concern, but does 'no ground rod' include the tranformer enclosure?

 

[augie47]

And no neutral conductor in the lateral, right? No need for 277v??

None no need for 277

Is it large enough to think of 230.95 GFP??

no 600 amp

Probably not our concern, but does 'no ground rod' include the tranformer enclosure?

not sure.. no ground to XO..enclsoure may have rod

 

[dbuckley]

Probably not our concern, but does 'no ground rod' include the tranformer enclosure?

I would say no; the transformer metalwork should be grounded (albeit probably not very well if its just a couple of rods) to prevent the tranny itself from becoming a hazard. Likely to become energized and all that jazz.

 

[benaround]

If the system is not grounded at any point, I would say it's ok.

 

[winnie]

I would suggest that the customer consider a resistance grounded system rather than an ungrounded system.

You have the same restrictions (line-line loads only, proper supervision, ground fault detection) and the same benefits (a single fault doesn't cause things to trip out) but you get the additional benefit of providing a solid voltage reference. During some types of faults on ungrounded systems you can get extremely high phase to ground voltage, which can damage other parts of the system.

-Jon

 

[jamesoftn]

The transformer has ground rodS at the transformer itself. These are the only ones. NO Electrodes at the building.

 

[don_resqcapt19]

The transformer has ground rodS at the transformer itself. These are the only ones. NO Electrodes at the building.

The code requires a grounding electrode system at the building. The only real difference in the grounding rules for grounded and ungrounded systems is that the grounded system has a main bonding jumper and the ungrounded system does not.

 

[pfalcon]

I would suggest that the customer consider a resistance grounded system rather than an ungrounded system.

You have the same restrictions (line-line loads only, proper supervision, ground fault detection) and the same benefits (a single fault doesn't cause things to trip out) but you get the additional benefit of providing a solid voltage reference. During some types of faults on ungrounded systems you can get extremely high phase to ground voltage, which can damage other parts of the system.

-Jon

As Jon suggested. High Impedance Wye.
As a follow up they will also need to establish a building ground grid which is not trivial.