Short to ground tripping 1200 amp bolt-loc switch

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Davebones

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Had a 15 amp ( 480 V ) tank immersion heater short to ground . This tripped the Main 1200 amp bolt- loc switch that feeds 3 panels before the heater . We reset the ground -fault on the 1200 amp Bolt-Loc switch and powered everything back up . The heaters are protected by JTD fuses . We know the Bolt-Loc saw the short to ground and tripped .Questioning why would the fuse's not open on this short to ground ? Would we want to use faster acting fuses for the heaters ? Also would we not want a coordination study done so a ground fault does not open all the way back to the 1200 amp bolt-loc switch ?
 

iwire

Moderator
Staff member
Location
Massachusetts
What I see all the time is that the GFP settings have been left at the lowest current, fastest response time pretty much ensuring a simple branch circuit ground fault can drop out a main.

Yes you will need a coordination study done to find out what the GFP should be set to.
 

zog

Senior Member
Location
Charlotte, NC
Had a 15 amp ( 480 V ) tank immersion heater short to ground . This tripped the Main 1200 amp bolt- loc switch that feeds 3 panels before the heater . We reset the ground -fault on the 1200 amp Bolt-Loc switch and powered everything back up . The heaters are protected by JTD fuses . We know the Bolt-Loc saw the short to ground and tripped .Questioning why would the fuse's not open on this short to ground ? Would we want to use faster acting fuses for the heaters ? Also would we not want a coordination study done so a ground fault does not open all the way back to the 1200 amp bolt-loc switch ?
Is the 1200A bolt-loc the only OCPD with GFP? I am guessing it is, common "cost savings" design for smaller facilities. Sounds to me like the system responded just as it was designed to.
 

iwire

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Location
Massachusetts
Is the 1200A bolt-loc the only OCPD with GFP? I am guessing it is, common "cost savings" design for smaller facilities. Sounds to me like the system responded just as it was designed to.
Very common in many facilities and yet we still get coordination studies done that seem to cure a simple groundfault in a branch or feeder from taking out the single main GFP device.
 

zog

Senior Member
Location
Charlotte, NC
Very common in many facilities and yet we still get coordination studies done that seem to cure a simple groundfault in a branch or feeder from taking out the single main GFP device.
If the main is the only breaker with GFP there is not much to coordinate.
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
If the main is the only breaker with GFP there is not much to coordinate.
That would depend on the rating of the branch circuit OCPD. The breaker in this thread is only 15 amps, so there should be no problem setting the trip level and time for the main GFP high enough that a fault on the load side of the 15 amp breaker will not cause the main GFP to operate. (based on a coordination study, of course)
 

don_resqcapt19

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Location
Illinois
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retired electrician
I see no mention of a 15A breaker, am I blind?
It said a 15 amp heater and I jumped to a 15 amp breaker. On a closer reading the 15 amp heater is protected by fuses, and I would expect that you could get coordination between those fuses and the GFP on the 1200 amp feeder.
 

iwire

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Location
Massachusetts
If the main is the only breaker with GFP there is not much to coordinate.
You have said this to me before and I did not understand your position at that time either.

All over current devices connected to grounded systems provide ground fault protection. It may not be adjustable but it has a value that can be used to attempt coordinating it with the main GFP
 

jim dungar

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Location
Wisconsin
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Retired Electrical Engineer - Power Systems
I have no problem believing that when set to 'minimum' a service entrance GF device will trip before a 15A branch device. This lack of coordination is probably the most common reason people try to 'cheat' service entrance GF protection.
 

brian john

Senior Member
Location
Leesburg, VA
I had a site last week the control power were off the the phase loss relay. blown fuse trip and GFP. Easier to shut it off than determine the source of the trip.


While one has to be careful making any recommendations regarding GFP settings. It is my belief that, the majority of CBs in a building are 20 and 30 amp, if you set the GFP relay at 400 amps and .1 second delay, you get out side the curve of most 20 and 30 amp CBs. Minimizing problems, until such time that the engineer can determine the correct settings (WHICH SELDOM TO NEVER HAPPENS)
 

iwire

Moderator
Staff member
Location
Massachusetts
I steadfastly refuse to even touch the settings without a report.

In most all instances where I deal with this someone is already contractually obligated to provide the report and simply has not done it. Once the breaker opens a couple of times and causes lost business the report suddenly gets done. My feeling is that if I band-aid the issue it will never be properly addressed.
 

brian john

Senior Member
Location
Leesburg, VA
I steadfastly refuse to even touch the settings without a report.

In most all instances where I deal with this someone is already contractually obligated to provide the report and simply has not done it. Once the breaker opens a couple of times and causes lost business the report suddenly gets done. My feeling is that if I band-aid the issue it will never be properly addressed.
In this area better than 85% never had a report done and the engineers steadfastly refuse to do a report saying it is not their job. Of the 85% about 2/3's are left at minimum setting, by the installing contractor, of that maybe 10% are disconnected.

I
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
If a arc flash study has been completed it will need to be re-evaluated if you turn up the GFP settings.
No it won't.

GFP settings are not considered when performing arc flash calculations.

However if 'phase' settings are changed on a downstream the arc flash results may need to be revisited.
 

zog

Senior Member
Location
Charlotte, NC
No it won't.

GFP settings are not considered when performing arc flash calculations.

However if 'phase' settings are changed on a downstream the arc flash results may need to be revisited.
Arrg, you are correct, I shouldn't post before I have my morning coffee. My mind usually goes right to arc flash when I hear "tweaking of settings"
 
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