Why would disconnecting both branch circuit conductors and the factory wired neutral from the neutral bar in the panel, cause an arcing effect that would trip a 200 amp main when the breaker is energized and the test button is pressed? The breaker is a Siemens 2 pole 50 amp being utilized for heating elements so there is not a neutral conductor attached to the breaker from the field.
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GFCI breakers 3
- Thread starter viperone
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I depressed the test button with both branch circuit conductors removed from the breaker, also the line neutral on the breaker had been removed from the neutral bar in the panel, there is not a field neutral installed as the breaker supplies a heating element and no neutral is necessary, the breaker arced internally and caused the main breaker for the panelboard to trip at the main switch gear. Any information on the cause and effect of this arcing would be appreciated. Thank you in advance for your replays.
I assume that you're using a suitable 2-pole breaker for your heater. If not, then...
Even though the load doesn't require the neutral because it is a heater, the GFI breaker does have a neutral wire - so why not hook it up ? These GFI breaker have circuitry inside and I would assume that the internal circuits would require power and would therefore require connection to the neutral.
On the GFI breakers that I've seen (single pole, 15 amp), the test button appears to imbalance the current transformer and thus cause the breaker to trip. I don;t believe that the test button actually shorts out any significant current (but standby for corrections).
If you're repeatedly tripping a 200-A main breaker, then you might want to consider calling in a licensed electrician. If I were your assistant, then I'd be taking an extended lunch break and some vacation until you're done with constantly tripping 200-A breakers. I'd take it as a 'sign'.
Even though the load doesn't require the neutral because it is a heater, the GFI breaker does have a neutral wire - so why not hook it up ? These GFI breaker have circuitry inside and I would assume that the internal circuits would require power and would therefore require connection to the neutral.
On the GFI breakers that I've seen (single pole, 15 amp), the test button appears to imbalance the current transformer and thus cause the breaker to trip. I don;t believe that the test button actually shorts out any significant current (but standby for corrections).
If you're repeatedly tripping a 200-A main breaker, then you might want to consider calling in a licensed electrician. If I were your assistant, then I'd be taking an extended lunch break and some vacation until you're done with constantly tripping 200-A breakers. I'd take it as a 'sign'.
Guys,
If it's a GFCI breaker (for personnel protection), the test button should initiate a current to ground of something like 15 milliamps (thus causing a trip).
If it's arcing with no load connectec, there must be something faulty inside the breaker that is allowing either a phase to ground or phase to phase fault to happen as it's opening. I'd toss it out and put in a new one. Shouldn't be any need for neutral connection, just ground.
Let us know what you find out!
Old Dave
If it's a GFCI breaker (for personnel protection), the test button should initiate a current to ground of something like 15 milliamps (thus causing a trip).
If it's arcing with no load connectec, there must be something faulty inside the breaker that is allowing either a phase to ground or phase to phase fault to happen as it's opening. I'd toss it out and put in a new one. Shouldn't be any need for neutral connection, just ground.
Let us know what you find out!
Old Dave
VE1BLL,
I stand corrected! Sorry about that, guys. I guess it comes from age and sitting in an office too long...
So, if viperone's breaker has its neutral wire disconnected, there may be more to the story that we don't know. I'd like to see a diagram of how a two-pole GFCI senses ground faults, if anyone has such.
Old Dave
I stand corrected! Sorry about that, guys. I guess it comes from age and sitting in an office too long...
So, if viperone's breaker has its neutral wire disconnected, there may be more to the story that we don't know. I'd like to see a diagram of how a two-pole GFCI senses ground faults, if anyone has such.
Old Dave
Ah, now it is coming back.
The load's neutral is connected to the GFI breaker's neutral screw terminal (the breaker has a neutral screw terminal in addition to the usual hot screw terminal). The breaker's neutral screw terminal is connected through the breaker to the panel's neutral bar via that attached white wire that I mentioned earlier.
Internally, the GFI breaker uses a current transformer (core) and associated circuitry (?) to measure the difference in the hot and neutral currents - if the difference exceeds a few mA (must be a ground fault), then it trips the breaker.
For a 2-pole GFI breaker, it must use the two hots in a similar manner (not sure if they would include the neutral as well - should be able to...).
The load's neutral is connected to the GFI breaker's neutral screw terminal (the breaker has a neutral screw terminal in addition to the usual hot screw terminal). The breaker's neutral screw terminal is connected through the breaker to the panel's neutral bar via that attached white wire that I mentioned earlier.
Internally, the GFI breaker uses a current transformer (core) and associated circuitry (?) to measure the difference in the hot and neutral currents - if the difference exceeds a few mA (must be a ground fault), then it trips the breaker.
For a 2-pole GFI breaker, it must use the two hots in a similar manner (not sure if they would include the neutral as well - should be able to...).
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The breaker has been replaced. I am a licensed electrician of 12 years and have never seen any thing like this happen before. I was unable to find much of anything about this occurrence in traditional text and so turned to the experts here. I am aware of how a GFCI, either single or multiple pole, senses faults and trips. And as such am confused as to why it arced internally, threw flames out of the breaker and tripped the main. The line neutral had been disconnected by a maintenance man and it was my fault for not seeing it before I proceeded further.
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viperone,
This is a strange one, so I'm guessing here. The GFI test button must take Current from one leg to energize the GFI current circuit. If there is no ground to sink the current is it possible that you are overvoltaging the insulation (Low side)and breaking down causing a small flash (ionazation)thats causing a break down of one or both of the legs?
-elf
This is a strange one, so I'm guessing here. The GFI test button must take Current from one leg to energize the GFI current circuit. If there is no ground to sink the current is it possible that you are overvoltaging the insulation (Low side)and breaking down causing a small flash (ionazation)thats causing a break down of one or both of the legs?
-elf
"...threw flames out of the breaker..."
Sounds exciting, glad you're okay.
I wonder if disconnecting the neutral causes some imbalance (drifting common) within the internal power supply. It probably draws power from both hot legs for safety reasons & redundancy. Perhaps it uses the old series capacitor extraction technique (times two) and one of the caps was damaged due to the disconnected neutral (too much voltage due to the drifting common) and the cap shorted out. Then you pressed the Test button and it put too much power into some part of the circuit and it blew up.
If I were you, I'd ask manufacturer if this is a known issue (disconnecting the neutral and then pressing the Test button). If they deny it is an issue and you're still interested, then you could try to replicate the incident (perhaps using a 4-foot long wooden stick to press the Test button this time...).
If it is a repeatable failure mode and they're unaware of it, then you'll be doing a service to everyone to draw attention to it. If true, then they should (at the very least) include a warning sticker for the panel.
Better yet, redesign the internal PS circuit.
Then again, maybe it was just a one-off failure.
Sounds exciting, glad you're okay.
I wonder if disconnecting the neutral causes some imbalance (drifting common) within the internal power supply. It probably draws power from both hot legs for safety reasons & redundancy. Perhaps it uses the old series capacitor extraction technique (times two) and one of the caps was damaged due to the disconnected neutral (too much voltage due to the drifting common) and the cap shorted out. Then you pressed the Test button and it put too much power into some part of the circuit and it blew up.
If I were you, I'd ask manufacturer if this is a known issue (disconnecting the neutral and then pressing the Test button). If they deny it is an issue and you're still interested, then you could try to replicate the incident (perhaps using a 4-foot long wooden stick to press the Test button this time...).
If it is a repeatable failure mode and they're unaware of it, then you'll be doing a service to everyone to draw attention to it. If true, then they should (at the very least) include a warning sticker for the panel.
Better yet, redesign the internal PS circuit.
Then again, maybe it was just a one-off failure.
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It could have just been a failure in the internal insulation in the breaker when it opened - unrelated to the GFCI function. In any breaker, an arc is created when the contacts open - sometimes the arc finds another current path other than the opening contacts.
These little breakers are pretty reliable, but cost competition is fierce and sometimes defects do occur.
I don't see an obvious reason why the open neutral would have cause a failure of this magnitude. This would seem to have more to do with the "business-end" of the breaker, not the GFCI electronics or shunt trip.
Another good reason to wear your arc-flash PPE whenever the panel door is open - even at 240V.
These little breakers are pretty reliable, but cost competition is fierce and sometimes defects do occur.
I don't see an obvious reason why the open neutral would have cause a failure of this magnitude. This would seem to have more to do with the "business-end" of the breaker, not the GFCI electronics or shunt trip.
Another good reason to wear your arc-flash PPE whenever the panel door is open - even at 240V.
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- #14
Thank you for your responses and insight into this matter, it has given me some views I hadn't thought of. The breaker has been tested and does continue to operate properly with associated wiring attached, but as yet I haven't simulated the conditions that created the fault. I will take your advice VE1BLL and contact the manufacturer and have some dialog to determine if it is a known occurence. I'll keep you posted on what I find and please continue your input.
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