GFCI Breakers tripping

[Chaosiscash]

We are having a GFCI trip problem lately and I was hoping someone would have some ideas.

Basically, for a few years we have bought "power carts" from a local vendor. These carts consist of a 480V disconnect fed from a welding-type plug. The disconnect feeds a 480V-208Y/120V transformer which feeds a lighting panel. This panel is loaded with 20A 120V GFCI breakers which feed receptacles mounted along the outside of the panel enclosure.

These carts are portable, and can be moved to various places in the building and connected to construction power to provide local 120V power for the various power hand tools used in demolition of the building. The building's roof leaks, a lot, so all of the enclosures are NEMA 3R and the recepts are water-proof. We have been using these for several years with no problems.

With the latest batch of about 20 or so of the carts, we have been having nuisance tripping problems. When we first plug the carts in, often times a random number (from one to all) of the GFCI breakers will trip, even with no tools plugged into the recepts. Or sometimes they will hold for a few hours and then randomly trip. Also, there is seemingly no pattern as to what source they are connected to or which breakers trip. The breakers will generally reset correctly, but then trip again a few hours later.

There have been no changes is the type of parts used on the carts, and the vendor is investigating their assembly quality for any issues.

Any ideas of what could cause this are greatly appreciated. Let me know if I left out any key info, I tried to give a much background as I could think of, but I'm sure I missed something.

Thanks in advance.

 

[Skogsgurra]

I think that one important parameter is missing in your description; the trip level. Is it 10 mA, 30 mA or some other current?

And, do they really trip when no load connected? Not even a plug and a cable?

If that is so, and no frequency inverters involved, I can't help but thinking that it is entirely the supplier's problem.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Chaosiscash]

They are Siemens 120V bolt-in GFCI breakers, which have a standard GFCI trip of 4-6 mA.

I agree it's probably a supplier problem, but it's slowing us down significantly, so if we can come up with a reason/fix, all the better.

Thanks for the reply.

 

[Skogsgurra]

Are you sure you had 4 -6 mA in the ones that worked? It is an awfully low trip level. Building sites normally can't even use 30 mA.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Skogsgurra]

But if you have one RCD per receptacle, it may work. And 30 mA disconnecting in 100 milliseconds (the standard spec) is safe for people.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Chaosiscash]

Skogs,

Good questions. Yes, they are useing the same breaker setup as the earlier carts. I agree the setting is very low. But its a government job, and the safety culture is, well, I don't want to use the word excessive, but let's just say it's overly conservative. But like I said, they are even tripping at no load, nothing even plugged in, so I'm thinking there is some sort of leakage to ground elsewhere.

Thanks again for all the help.

 

[Skogsgurra]

Where are you in the world?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[patrick7]

sounds simple to me, nothing pluged in = defective.

 

[patrick7]

just a thought here. i have seen this one strand on the conductor wire was not landed correctly and allowed a path for the leakage to trip the breakers.
sorry i didnt remember that earlier.

 

[davidbeach]

Gunnar, Sounds like standard US practice, here 'bouts 30mA is not acceptable for protection of people.

Sounds like patrick7 is on to something, there is a leakage path somewhere or the breakers are defective.

 

[Skogsgurra]

Yes, that's why I wondered where in the World. If in US, I think thare's not much to do about it. Open the boxes and dry out some humidity perhaps?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Is there any influence on the new power carts that does not apply to the older units?
Use in different area with higher relative humidity and possibly airborn contaminants?
A different or new supply system that may be supplying non-sinulsoidal wave forms?
Is there any equipment in use in the same area as the new carts that may be generating harmonics?
Lastly, I suggest getting some resistors and checking whether the new GFCIs are tripping below spec.
120 V/.001 A = 120 kilo-ohms. I would test with a 120K, a 56K, and a 39K resistor. The breaker should hold in for all three values. That should give about 1 ma, 2 ma, and 3 ma respectively.
Before condemming the new equipment, check side by side with an older "No problem" cart. Check in both the new area and the old area. If the new carts are running on a new supply there may be a problem with transient voltage spikes.
respectfully

 

[ScottyUK]

Gunnar - 30mA and 100ms delay for personnel protection?

In the UK anything with an definite minimum delay is for equipment protection only; 30mA instantaneous trip is required for personnel protection, with 10mA instantaneous trip in higher risk areas. Are the rules different in Sweden? I thought Europe was one big happy family after we adopted the new colours and confused the UK's electricians!


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Sometimes I only open my mouth to swap feet...

 

[powerjunx]

scott, i guess such difference was already harmonized and complied to the working standards.







"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.

 

[Chaosiscash]

Folks,

Sorry its taken so long for me to get back, been out of the office a couple of days.

Skogs, I'm in the US.
Patrick, good idea, I'll have the guys double check all the "factory" terminations.

Waross, good suggestions. The new carts are in the same environment as the old, we've actually had a new cart plugged into the same bus in the same area and seen it trip, where the old one was fine. And the only equipment on the services are the carts themselves (and their 120V loads). We may have a humidity problem, but only if the GFCIs have gotten more sensitive than the old setup, which seems odd.

Thanks for all the help and suggestions. I'll try and let you know what I find.

Chaos

 

[BobbyNewmark]

Has anybody used black rubber tubing as an electrical insulator? A lot of that tubing uses carbon black as a filler and is surprisingly conductive.

What happens if you swap an old GFCI outlet into a new cart, and vice versa?

 

[JBinCA]

Noting on the line side of the breakers should contribute to the GFCI tripping, so I wouldn worry about checkig out wiring on that side.

Single strands of multi-strand wiring shorting from terminal to terminal could account for trippin on one or two breakers, but not a likely cause for your situation (unless your electrician has A.D.D).

I'd say your problem is in the breakers themselves.

I'm surprised no one has asked whether it's always the same few breakers that trip over and over, but that's what I'd expect if the problem is a lot of BKRs with a higher than usual failure rate.

To sum it up - I agree with patrick7 - "sounds simple to me, nothing pluged in = defective"

Regards,

JB