To add to my thread of medium voltage grounding comes another one low voltage (240V) delta. I saw another set of prints the other day (I don't know why all of a sudden I am seeing ungrounded systems multiple times in the span of a couple of weeks) the one-line indicates a 240V-Delta service (ungrounded) the 240 is derived via a 480-240V xfmr (75kva) to a 240V switch and fuse panelboard. I guess I do not understand why ungounded??? I understand this is a facility that deals with motors (reparing / manufacturing not entirely sure) but would not a corner ground at a minimum be best? or if service continunity is a real issue a HRG? I would imagine you have the same issues as with a medium voltage system and the elevated arcing ground faults regardless of the voltage system espically if we are dealing with motors? can you do a HRG system on a 240V system? if you go ungrounded the first ground fault will estalbish a reference point to ground (correct)? so you would need at a minimum ground fault detection at the main? however you would not know what feeder this is on or would you be required to have ground fault indication on all indivigual branches?? dose not make any sense to me just curious on everyones thoughts..thanks.
240V-Delta
- Thread starter Mike01
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250.21(A) lays out the conditions that must be satified to operate a system ungrounded. 250.21(B) requires ground detection for these systems. (2008 code)
The limit on an HRG is on higher system voltages where capacitive charging current exceeds the limit for an HRG. IOW, no problems with an HRG at this voltage. It could even help locate the fault if equipped with a pulser.
You would need ground fault indication in one location only. If I had one on each feeder they would all always show the same condition. A ground fault in one location would set off all the indicators.
The limit on an HRG is on higher system voltages where capacitive charging current exceeds the limit for an HRG. IOW, no problems with an HRG at this voltage. It could even help locate the fault if equipped with a pulser.
You would need ground fault indication in one location only. If I had one on each feeder they would all always show the same condition. A ground fault in one location would set off all the indicators.
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