Ungrounded MV System - NFPA

[ukgraduate]

Hello,

Can someone please tell me if an ungrounded 13.8kV system is allowed by the NFPA/NEC requirements.

I have read the NEC code but cannot find any definite answer.I may be missing something ofcourse.

Can anyone please advise and hopefully point to the specific article.

Thanks

 

[wroggent]

Check 250.20(C). Not required unless it serves mobile or portable equipment.

 

[ukgraduate]

Thankyou for that.

Do all ungrounded systems require earth fault detection?

Would a 13.8kV ungrounded system require one?

Also can someone provide a link or brand/model of equipment that has ground fault detection at MV

 

[Parchie]

Really depends on the insulation rating of your equipment. IIRC, you are not required to trip the system if your insulation is rated 173% of the system voltage. You can set your ground fault detection to alarm and locate the faulted section. If your equipment voltage rating is 133% of the system voltage, you are required to set your ground fault protection to alarm and time the tripping within 1 minute to an hour. If your insulation ratings are 100% of the system voltage, you are required to alarm and trip the system within 1 minute before your equipment gets damaged by overvoltages.