480 v. DELTA
- Thread starter tweekster
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bphgravity
Senior Member
- Location
- Florida
Re: 480 v. DELTA
I am thinking you have a corner-grounded Delta where one phase conductor is intenionally grounded. Check to see if one of the three phases, probably "C" in your case is unfused in the main disconnect. If not, it should be. I believe the "B" phase is the proper phase to be grounded.
Edit: Sorry Roger, didnt see your post before I submitted.
[ August 30, 2004, 08:48 PM: Message edited by: bphgravity ]
I am thinking you have a corner-grounded Delta where one phase conductor is intenionally grounded. Check to see if one of the three phases, probably "C" in your case is unfused in the main disconnect. If not, it should be. I believe the "B" phase is the proper phase to be grounded.
Edit: Sorry Roger, didnt see your post before I submitted.
[ August 30, 2004, 08:48 PM: Message edited by: bphgravity ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: 480 v. DELTA
I don't know if you could call it normal, It is very common. But only if the "B" phase is grounded not "C" phase. And two pole breakers are used instead of three pole. Most industrial service's I have worked on use an ungrounded delta but have a ground detection system to alert plant operators that a phase has been grounded. This system is used when shut downs are not a good thing. It is still safe but just requires two conductors grounded before a OCPD opens. And since you said that "C" phase is the one grounded I would check to see if it is intentionally grounded via bond at the main service or it is unintentionally grounded and should be repaired. Also if the latter then a ground monitor should be installed so someone will know if this happens again.
I don't know if you could call it normal, It is very common. But only if the "B" phase is grounded not "C" phase. And two pole breakers are used instead of three pole. Most industrial service's I have worked on use an ungrounded delta but have a ground detection system to alert plant operators that a phase has been grounded. This system is used when shut downs are not a good thing.
It is still safe but just requires two conductors grounded before a OCPD opens. And since you said that "C" phase is the one grounded I would check to see if it is intentionally grounded via bond at the main service or it is unintentionally grounded and should be repaired. Also if the latter then a ground monitor should be installed so someone will know if this happens again.
electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
Re: 480 v. DELTA
I have worked with ungrounded delta systems too. 480volt mostly. Reliable and safe if properly maintained. But a ground fault detection system is mandatory IMO.
I have worked with ungrounded delta systems too. 480volt mostly. Reliable and safe if properly maintained. But a ground fault detection system is mandatory IMO.
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: 480 v. DELTA
I have a question in relation to this discussion...What are the advantages or disadvatnages of having a corner grounded delta system versus an ungrounded delta system? And how does a ground detection system detect ground faults on an ungrounded system? Hurk, you mentioned something about 2 connections to ground before OCPD opens, this confuses me. What happens with only one unintentional connection to ground happens? I understand that this is for systems that people do not want shut down, but how is the ground fault cleared in that case? Thanks for putting up with a newbie
Dave
I have a question in relation to this discussion...What are the advantages or disadvatnages of having a corner grounded delta system versus an ungrounded delta system? And how does a ground detection system detect ground faults on an ungrounded system? Hurk, you mentioned something about 2 connections to ground before OCPD opens, this confuses me. What happens with only one unintentional connection to ground happens? I understand that this is for systems that people do not want shut down, but how is the ground fault cleared in that case? Thanks for putting up with a newbie
Dave
- Location
- Massachusetts
Re: 480 v. DELTA
Say phase A faults to ground, all that will happen is a the ground fault indicator will operate. Every thing remains operational and safe, at this time the system should be checked to find and fix the ground fault.
If the phase A ground fault is allowed to remain the next ground fault of phase B or C will cause the overcurrent device to operate causing an unwanted shut down.
With an ungrounded system the overcurrent device will not operate when the first ground fault happens.Originally posted by wirenut1980:
something about 2 connections to ground before OCPD opens, this confuses me. What happens with only one unintentional connection to ground happens? I understand that this is for systems that people do not want shut down, but how is the ground fault cleared in that case? Thanks for putting up with a newbie
Dave
Say phase A faults to ground, all that will happen is a the ground fault indicator will operate. Every thing remains operational and safe, at this time the system should be checked to find and fix the ground fault.
If the phase A ground fault is allowed to remain the next ground fault of phase B or C will cause the overcurrent device to operate causing an unwanted shut down.
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: 480 v. DELTA
And fixing the ground fault would require working on an energized circuit? How would one clear the fault in this case when everything is still energized? Or does the fault clear itself somehow?
And fixing the ground fault would require working on an energized circuit? How would one clear the fault in this case when everything is still energized? Or does the fault clear itself somehow?
- Location
- Massachusetts
Re: 480 v. DELTA
Could it be done live?
Yes that probably happens.
But you could also schedule a shut down to find the problem. Simply turning off feeder breakers one at a time until the ground fault indicator light goes out would localize the fault to a panel, then a little testing for continuity to ground on each branch circuit in that panel.
A scheduled shutdown is easer to take than an unscheduled shutdown and the damage caused by a line to line fault if the first ground fault is not fixed.
Could it be done live?
Yes that probably happens.
But you could also schedule a shut down to find the problem. Simply turning off feeder breakers one at a time until the ground fault indicator light goes out would localize the fault to a panel, then a little testing for continuity to ground on each branch circuit in that panel.
A scheduled shutdown is easer to take than an unscheduled shutdown and the damage caused by a line to line fault if the first ground fault is not fixed.
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: 480 v. DELTA
Yes that does make more sense . Thank you!
Yes that does make more sense
. Thank you!- Status