ground fault tripping

[jim dungar]

Mostly because they are "privately owned" - staff brings them from home and plugs them in. I wouldn't be surprised if the report causes management to introduce a "no space heaters" policy.

In my experience portable 'under the desk' space heaters do not cause nuisance tripping of GF, however they do cause overloaded branch circuits.

My comments concerning heaters has to do with 'fixed' units, such as HVAC duct heaters.

 

[ATSman]

Nuisance Trips

Nuisance Trips

You guys are a great resource. Thank you, sincerely. Having sorted through the responses, done a little more research (including reading BrianJohn's great 2008 thread on the topic) and talked amongst my peers I have a few follow-up items:

1. As near as we can tell there is no reason for the GFP in the 208V distribution panel. We suspect it was poor design. The only existing loads fed off this panel are office areas, gymnasium areas, and a few mechanical room/loading dock areas. The only new loads are for fitness equipment that was not yet on site at the time of the event.
2. The GFP device is an ITI BGFL-259-1200, installed circa 1999. I reviewed the literature, it doesn't come out and say it but FWIW I assume this is a zero sequence system.
3. The existing breakers are Siemens, I assume type BL breakers. Judging by the 1998 drawings most are 20A/1P.

I was leaning towards cranking the settings to the max, but after plotting the GFP with the 20A/1P breaker on a TCC I see how the minimum settings could have caused a trip. Cranking it up to 300A or 400A would put some space between them. I will recommend 400A, say with a brief explanation why I ~think~ it will solve the problem, and add if they are serious about 100% avoidance there are a number of measures they may find worth taking.

So that's the direction I'm headed. Beyond that I have a few more what-if questions...
4. Is it correct to say (assuming correct wiring techniques were used) that whatever caused the GFP to trip was something on the secondary side of the delta-wye transformer, possibly including a failure in the GFP itself? That an event on the primary side would not have passed through to the secondary?
5. And vice versa - if we effectively disabled the 208V GFP could we assume if an event repeated itself on the 208V side that there is virtually no chance it would now trip out the main 480V GFP?
6. What is worst-case scenario if we cranked up the GFP settings to the max? The GFP is for equipment protection, not personnel protection, correct? Is it possible that cranking up the settings would expose personnel to a life-safety hazard that would otherwise be avoided?
7. Do I read correctly that space heaters are often the source of intermittent ground faults? The day in question was not a particularly cold day (mid 30s, when it has been below zero quite a bit this month). But I was told there may have been almost a dozen electric space heaters in use at various workstations.

Thanks again for the excellent insight!!

One other cause, and I don't recall it being mentioned here, is nuisance tripping. With solid state devices such as GF relays, Protective Relays used in MV, and breaker trip units that are 10 years or older can send false signals to trip open the circuit. This can occur without any fault, either phase to phase or phase to ground, on the system. Some say that the electrolytic capacitors used in the power supplies begin to fail causing the miss-firing. We find this common with GFR built by GE, Westinghouse, Hi-Z, ITE, etc. The only fix is to replace the GF relay and injection test the system for functionality. This is another option you have in this process of elimination but may solve the problem.

 

[brian john]

Brian
I cannot see your reasoning either. These are 2 separately derived systems: 480V & 208V with separate transformers.
Any ground current on a fault will only flow back to the lowest potential of it's own source transformer: The X0 connection of the secondary winding. In this loop how can it cross over to another system? That would rewrite Kirchoff's Law!
Pls explain. :?

Neutral from the the 208/120 VAC system is in a common junction box with a neutral from the 480/277 VAC system, the neutral are crossed. So lets assume you have a 277 VAC branch circuit neutral tied to the neutral of the 208/120 VAC branch circuit. THe current travels on the branch circuit neutral to the XO on to the neutral ground bond and back to the source on the EGC.

Ask me how hard it was to find this issue. I have seen this more that once.

 

[brian john]

You guys are a great resource. Thank you, sincerely. Having sorted through the responses, done a little more research (including reading BrianJohn's great 2008 thread on the topic) and talked amongst my peers I have a few follow-up items:

1. As near as we can tell there is no reason for the GFP in the 208V distribution panel. We suspect it was poor design. The only existing loads fed off this panel are office areas, gymnasium areas, and a few mechanical room/loading dock areas. The only new loads are for fitness equipment that was not yet on site at the time of the event.
2. The GFP device is an ITI BGFL-259-1200, installed circa 1999. I reviewed the literature, it doesn't come out and say it but FWIW I assume this is a zero sequence system.

ITI or Electro Magnetics BGFL relays are typically zero sequence.

3. The existing breakers are Siemens, I assume type BL breakers. Judging by the 1998 drawings most are 20A/1P.

4. Is it correct to say (assuming correct wiring techniques were used) that whatever caused the GFP to trip was something on the secondary side of the delta-wye transformer, possibly including a failure in the GFP itself? That an event on the primary side would not have passed through to the secondary?

Correct, assuming you have no crossed neutrals

5. And vice versa - if we effectively disabled the 208V GFP could we assume if an event repeated itself on the 208V side that there is virtually no chance it would now trip out the main 480V GFP?

Correct, assuming you have no crossed neutrals

6. What is worst-case scenario if we cranked up the GFP settings to the max? The GFP is for equipment protection, not personnel protection, correct? Is it possible that cranking up the settings would expose personnel to a life-safety hazard that would otherwise be avoided?

It would expose your equipment to more damaged could result in additional damage to surrounding equipment or personnel.

7. Do I read correctly that space heaters are often the source of intermittent ground faults? The day in question was not a particularly cold day (mid 30s, when it has been below zero quite a bit this month). But I was told there may have been almost a dozen electric space heaters in use at various workstations.

Not that I know of, otherwise they would be noted as causing branch circuit breakers to trip in the absence of GFPE>

 

[brian john]

One other cause, and I don't recall it being mentioned here, is nuisance tripping. With solid state devices such as GF relays, Protective Relays used in MV, and breaker trip units that are 10 years or older can send false signals to trip open the circuit. This can occur without any fault, either phase to phase or phase to ground, on the system. Some say that the electrolytic capacitors used in the power supplies begin to fail causing the miss-firing. We find this common with GFR built by GE, Westinghouse, Hi-Z, ITE, etc. The only fix is to replace the GF relay and injection test the system for functionality. This is another option you have in this process of elimination but may solve the problem.

HI-Z, wow that goes a long way back I use to deal with them quite a bit, called them one day and I think it was the son of the owner telling me the chief engineer passed away and HI-Z relays were no longer available.

Many years ago another test company reported to us that they had been monitoring a relay for nuisance tripping and when they had a high level impulse on the control circuitry the GFPE would call for a trip. The relay was a Brown Boveri and was maybe 8-12 years old at the time, they replaced the relay with a new relay, same manufacture and then problem stopped. The old relay had been tested for proper trip operation (current pick up at all factory presets for current and timed operation at the as found setting).

 

[brian john]

In my experience portable 'under the desk' space heaters do not cause nuisance tripping of GF, however they do cause overloaded branch circuits.

My comments concerning heaters has to do with 'fixed' units, such as HVAC duct heaters.

VAV with resistive heaters are notorious for tripping GFPE and then locating the right VAV becomes a chore.

 

[hurk27]

Missed read Brians post

 

[ATSman]

HI-Z, wow that goes a long way back I use to deal with them quite a bit, called them one day and I think it was the son of the owner telling me the chief engineer passed away and HI-Z relays were no longer available.

Many years ago another test company reported to us that they had been monitoring a relay for nuisance tripping and when they had a high level impulse on the control circuitry the GFPE would call for a trip. The relay was a Brown Boveri and was maybe 8-12 years old at the time, they replaced the relay with a new relay, same manufacture and then problem stopped. The old relay had been tested for proper trip operation (current pick up at all factory presets for current and timed operation at the as found setting).

Thanks BJ
I was begining to think I was the only one who saw this.

 

[brian john]

Thanks BJ
I was begining to think I was the only one who saw this.

Over the years we have added a few that randomly tripped for no specific reason. This is a costly investigation to find nothing. We replaced the GFPE relay and the problem disappeared.

Additionally DO NOT Megger the controls with the GFPE, Phase Failure, UV/OV relay connected.

 

[ATSman]

Over the years we have added a few that randomly tripped for no specific reason. This is a costly investigation to find nothing. We replaced the GFPE relay and the problem disappeared.

Amen to that.

Additionally DO NOT Megger the controls with the GFPE, Phase Failure, UV/OV relay connected.

Also disconnect solid state trip unit (pull connection plug) on C-H LV Air Frame breakers before megger.

 

[kwired]

Neutral from the the 208/120 VAC system is in a common junction box with a neutral from the 480/277 VAC system, the neutral are crossed. So lets assume you have a 277 VAC branch circuit neutral tied to the neutral of the 208/120 VAC branch circuit. THe current travels on the branch circuit neutral to the XO on to the neutral ground bond and back to the source on the EGC.

Ask me how hard it was to find this issue. I have seen this more that once.

I would think you will find it faster the next time you encounter it.

Seems to me once you suspect that as a potential problem you should be able to remove system bonding jumper and grounding electrode conductor(s) and check for continuity between both systems. If there is continuity, you then need to track down why and where.

 

[brian john]

I would think you will find it faster the next time you encounter it.

Seems to me once you suspect that as a potential problem you should be able to remove system bonding jumper and grounding electrode conductor(s) and check for continuity between both systems. If there is continuity, you then need to track down why and where.

The largest we had to investigate was a 26 story mid-rise, 4 risers, 8-12 panels in each closet, not including the penthouse and 3-750 UPS , 2-1750 kw generators, with distribution for a data center. I think we had 12 men 12-16 hours, 2.5 days. All off hours.

We have a system but it still takes time, isolate all neutrals in the switchboard, lift the neutral ground bond and meg, if the bus is clear, isolate all the branch circuits neutrals, (all CB's are open) meg the feeders, if they are clear start on the branch circuits.

We start at 50 VAC and increase for each test to minimize damaging equipment, find a branch circuit neutral shorted, tag it and move on. After the building is completed with all neutrals, then then men spilt into groups of two and look for the problems.