Ground Fault Indication 2400V Systems - NEC

[MrJLH]

Does anyone have any guidance on how to monitor a ground fault on a 2400 three phase system fed from an ungrounded delta-delta transformer?

Our facility previously installed a 2400V medium voltage motor control center. When the motor control center was installed, it was electrically fed from an existing three-phase three-wire ungrounded delta-delta transformer. The feeder to the 2400V MCC is approximately 200ft from the existing ungrounded delta-delta transformer. Do ask me why this was done this way. The switchgear drawings do not provide any details on ground fault indication.

NEC 250.21 covers systems 50 volts to 1000 volts not required to be grounded, but what about systems greater than 1000V?

 

[jim dungar]

Protection is usually provided by a multifunction relay. Does your switchgear have a single main breaker?

 

[MrJLH]

Protection is usually provided by a multifunction relay. Does your switchgear have a single main breaker?

There is a GE850 for the main. I don't see how the relay would pick up a ground fault given this is a ungrounded delta-delta.

 

[jim dungar]

Most relays are able to sum the 3 phase currents and trip if there is an excess unbalance.
You need to look at your 3-line diagram and see the CT interwiring and relay inputs.

Look at your relay options for 50G/51G or 50N/51N functions.