GF protection on Delta system

[donny baker]

I am looking at a 480Y/277 V switchboard on a 2500kva substation. However, there is no neutral bus installed any longer, it was reconfigured configured as a DELTA power system when the transformer burned up. A report from the PQ / grounding test company indicated that "this type of power system (DELTA) is required to have ground fault detectors installed." I do not see where this is required. Can anyone explain, or has experience with this?
(The Main Breaker is a SQ-D DSII 4000 AF, with long, short, ground, no inst. elements.)

 

[winnie]

I presume that you have an _ungrounded_ delta.

The _why_ for having ground fault detectors is that the first ground fault on an ungrounded delta won't trip any OCPD; ungrounded deltas are used to permit continued operation even with a single ground fault. However you need to detect this first ground fault so that you can correct it prior to a second ground fault developing.

The _how_ of such ground fault detection offers a vast number of possibilities.

The _simplest_ is just a set of incandescent lamps, connected in a 'wye' configuration with the 'neutral' grounded. In the event of a ground fault, the light on the faulted leg will go out. I don't know if you are now required to use a listed assembly for this sort of simple detector.

-Jon

 

[donny baker]

Yes, it comes back to me now. I remember about the line to ground voltage rise after the first fault. But no ground fault detection / location equipment is actually required per NEC, but just a darn good idea?

 

[jim dungar]

Yes, it comes back to me now. I remember about the line to ground voltage rise after the first fault. But no ground fault detection / location equipment is actually required per NEC, but just a darn good idea?

Ground detectors used to be optional.

They are now required per the last sentence in 250.21 of the 2005NEC.

 

[donny baker]

very well, thank you for you help.