Ground-Fault Protection for Equipment

[Volta]

It is 480/277v, 3000 amp, service rated disconnect, though not truly a service, but a main.

GE Power Break, TP 3030S, with an RMS-9 Micro Versa Trip. Circa 1987.

Does anyone have any advice before I go in to start looking for the ground-fault that caused it to operate?

 

[brian john]

It is 480/277v, 3000 amp, service rated disconnect, though not truly a service, but a main.

GE Power Break, TP 3030S, with an RMS-9 Micro Versa Trip. Circa 1987.

Does anyone have any advice before I go in to start looking for the ground-fault that caused it to operate?

Are you saying you had a ground fault and you are trying to isolate this possible ground fault?

1. What features does the CB OCP have Long time? Short time? Instantaneous? GFP?
2. What makes you think it was a GFP operation?
3.Can you get someone to perform Secondary injection or primary injection testing?
4. Did you or someone else reset the CB without determining the cause of the fault?
5. Did you check all downstream motors (Megger)?
6. Did you megger the feeder?
7. Did you check for downstream OCP (fuses or CB's) tripped/blown?
8. Were there any contractors working in the building doing renovations possibly tripping a 480/277 CB accidentally or intentionally.
9. What is the GFP settings?
10. If the system is back on can you measure the current on the neutral ground bond?
11. Did you megger the neutral to ground with the bond lifted.

 

[Volta]

Are you saying you had a ground fault and you are trying to isolate this possible ground fault?

Yes.

1. What features does the CB OCP have Long time? Short time? Instantaneous? GFP?

Long Time range= 1 to 4, set at 4
Instantaneous range= 1.5x to 10x, set at 3x
Current range= .5 to 1.0, set at 1.0
GF Pickup range= .25 to .375, set at .375
GF Delay range= I2T In / I2T Out, set to I2T Out Max

2. What makes you think it was a GFP operation?

Relatively low current draw, not measured, expect that it was 400 to 600 amps max, likely less.
Older building customer is moving into. Found many EGCs on neutral bars, most have been placed on new EGC terminals, not all yet.

3.Can you get someone to perform Secondary injection or primary injection testing?

IDK. Is that generally done on site or would that be sent out? If the pickup is faulty, is that the only reasonable way to find out? Thousands?

4. Did you or someone else reset the CB without determining the cause of the fault?

Yes.

5. Did you check all downstream motors (Megger)?
Not yet. One recently for other concerns, ok.
6. Did you megger the feeder?

Not yet. I plan to start from load sides of fused switches in switchgear, and work downstream. Thought I would skip the busbars within switchgear to start, but can go back to them after one or two levels of tracing.

7. Did you check for downstream OCP (fuses or CB's) tripped/blown?

Yes. Large building, checked many, less than all.

8. Were there any contractors working in the building doing renovations possibly tripping a 480/277 CB accidentally or intentionally.

Not really. The customer is still setting up, so some tools as a contractor would use, but few at the time. None of the large production equipment in use to my knowledge at that time, but circuits were energized.

9. What is the GFP settings?

As above.

10. If the system is back on can you measure the current on the neutral ground bond?

Unsure. I mean, yes, eventually, but want to have POCO deenergize to so we can maintain 13k disconnect outside before operating such. I doubt it has been used in 23 years. So a lot of coordination will be needed. Don't want to open main section hot . . . The service feeds a second main (208 wye), so they will lose power to that when service is opened. I want to postpone that as long as reasonable.

11. Did you megger the neutral to ground with the bond lifted.

Not 'till as above.

Can you explain these settings? Is the GF Pickup a percentage of the total OCP level, or of the 1200a permitted (now and in 1984)?

What current level of GF might we be seeing?

What is the difference between the Long Time Delay and the GF Delay? Is the Long for simple overcurrent?

Thanks.

 

[jim dungar]

The settings are all in multiples of the breaker sensor (3000A in your case), so .375x3000=1200A. The GF delay of MAX = .4secs.

Normally 1200A ground faults are easy to locate, by looking for the burn marks.

I think you need to have your breaker tested.

 

[shepelec]

Last time I had a GFP main tested it was around $900, all on site. Full function test, current injection and full report for the owners records.

 

[Volta]

The settings are all in multiples of the breaker sensor (3000A in your case), so .375x3000=1200A. The GF delay of MAX = .4secs.

Normally 1200A ground faults are easy to locate, by looking for the burn marks.

I think you need to have your breaker tested.

I wonder if these settings at the maximums (except Instantaneous) are original or were reset as a result of previous trips while the former owner occupied the space.

What is the Delay Out vs. the Delay In?

 

[brian john]

Testing is done on site; I would at a minimum do primary on the GFP and secondary for all other functions unless this is a draw out CB.

You need to measure the neutral ground bond current with the switch energized. Tough to do under today’s guide lines.

Compressors and motors are a big GFP item as coordination between their OCP and the GFP is almost impossible (depending on motor size)

Hot water heaters and VAV boxes are another item that can cause GFP trips and be difficult to locate.

Check the neutral wiring for the GFP Neutral CT, if there is a connection issue this can result in a trip and damage to the CT. I have seen this quite a few times.

If you have a GFP operation exceeding 1,125 amps (based on setting provided) and at .4 seconds damage should be evident somewhere (as Jim stated) with exception of hidden conductors such as motors and VAV's.


When trouble shooting GFP operations I always look in the gear first, PRIOR TO ENERGIZING, as a second fault in the gear can be bad for your health. In addition while I would not recommend this (re-energizing prior to locating problem/fault) but it is done. If you must reset the Main lower the GFP settings to minimum settings to minimize further damage.

Unless there is a neutral ground issue between the 208/120 distribution and the 480/277 distribution the issue will be somewhere in the 480/277 distribution.

Check for neutrals on the ground bus in the gear and for grounds on the neutral bus. Any cross connections downstream of the neutral CT will cause issues THOUGH 1,125 amps is a lot of issues had this level of ground current would be highly unusual, but possible.

If you get an outage megger all neutrals downstream from the main, start my lifting the neutral ground bond and then the feeder neutrals one at a time.

For primary of the FGP and secondary of all functions ST-980.00, OT 1,280.00 Primari injection of all functions vary but can run as high as 3,000.00-3,600.00this must be done on OT as the main is removed for testing.

 

[Volta]

Testing is done on site; I would at a minimum do primary on the GFP and secondary for all other functions unless this is a draw out CB.

It is not.

You need to measure the neutral ground bond current with the switch energized. Tough to do under today?s guide lines.

Yes. I am not an employee, but the laws of physics won't care.

Compressors and motors are a big GFP item as coordination between their OCP and the GFP is almost impossible (depending on motor size)

Hot water heaters and VAV boxes are another item that can cause GFP trips and be difficult to locate.

Check the neutral wiring for the GFP Neutral CT, if there is a connection issue this can result in a trip and damage to the CT. I have seen this quite a few times.

If you have a GFP operation exceeding 1,125 amps (based on setting provided) and at .4 seconds damage should be evident somewhere (as Jim stated) with exception of hidden conductors such as motors and VAV's.


When trouble shooting GFP operations I always look in the gear first, PRIOR TO ENERGIZING, as a second fault in the gear can be bad for your health. In addition while I would not recommend this (re-energizing prior to locating problem/fault) but it is done. If you must reset the Main lower the GFP settings to minimum settings to minimize further damage.

Agreed. I've been in the load sections of this gear recently, things looked good, but of course you are right, and things change. Precautions were certainly taken, but . . .
Can these settings normally be adjusted while energized?
If so, there is no way to be remote while doing so.

Unless there is a neutral ground issue between the 208/120 distribution and the 480/277 distribution the issue will be somewhere in the 480/277 distribution.

Good point. There is a mix of good and funky wiring there.

Check for neutrals on the ground bus in the gear and for grounds on the neutral bus. Any cross connections downstream of the neutral CT will cause issues THOUGH 1,125 amps is a lot of issues had this level of ground current would be highly unusual, but possible.

None previously observed, but will double check there. Very likely to exist in other areas of the building though.

If you get an outage megger all neutrals downstream from the main, start my lifting the neutral ground bond and then the feeder neutrals one at a time.

For primary of the FGP and secondary of all functions ST-980.00, OT 1,280.00 Primari injection of all functions vary but can run as high as 3,000.00-3,600.00this must be done on OT as the main is removed for testing.

Standard and over time? Removed but still on site? Standard pricing and/or your company (in your area)?

Also have found a notice of spurious tripping from the NRC in 1993 of the RMS-9. Reports may have all been with ungrounded systems.

 

[Volta]

GF Pickup range= .25 to .375, set at .375

I was sloppy when noting this, it it set to .37 S, which seems to be 'S' for Sensor Amp Rating.

 

[brian john]

So any luck on resolving the issue.

 

[Volta]

No. I will go Saturday, when they are not occupied. They only want to pay for a day's research at this point, so I guess I will try to determine that the first-level feeders after the switchgear are ok, and the switchgear itself if possible. I can turn off the main, but don't really want to open the incoming source, so may not be able to safely get to the MBJ or easily isolate anything in that area in the given time.

I found one 277 volt 20 amp breaker on a lighting circuit that has tripped in a less used area, so I'll meg that branch too.

Can't see the MBJ, but fear that it will be busbar and because of the width I won't have a means to measure the current.