# Square D QO GFI Breaker



## DCooper (Dec 6, 2011)

I ran into a situation yesterday, in a bathroom with three 6" cans with 75W par 30's and vent fan on 20A Square D QO GFI Breaker kept tripping. Anyone else ran across this? After much troubleshooting and saying  a lot. I decided to remove the bulbs. Sure enough the breaker didn't trip. Ended up replacing them with LED Conversions (which customer wanted anyway) and no more problems. Is this a common issue with incandescent on a gfi breaker?


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## electricmanscott (Feb 11, 2010)

There's an issue in one of the lights. Did you remove one lamp at a time to isolate the problem?


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## DCooper (Dec 6, 2011)

Yes. It didn't seem to matter which one or combination thereof. I think it was something with the incandescent bulbs. Maybe they were of lesser quality? The LED conversions solved the issue. Which I thought was odd. I just spoke to Square D Breaker support and they had no idea either, unless it was a lesser quality bulb causing the nuisance trip.


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## don_resqcapt19 (Jul 18, 2010)

I don't see how a two wire load can directly cause the GFCI to trip. There must be some issue with leakage current in the circuit.  Maybe a high resistance connection between the netural and the ground that will flow 5mA when the load (lamps are installed) is increased. The LEDs would have less load may keep the GFCI from tripping, but the original problem still exists.


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## 480sparky (Sep 20, 2007)

Why are the lights & fan on a GFCI to begin with?


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## DCooper (Dec 6, 2011)

480sparky said:


> Why are the lights & fan on a GFCI to begin with?


Fan manufacturer recommends it, and one light is over the tub.


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## woodchuck2 (Sep 18, 2009)

Replace the bulbs with better quality or a different manufacturer.


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## don_resqcapt19 (Jul 18, 2010)

woodchuck2 said:


> Replace the bulbs with better quality or a different manufacturer.


How would the bulb itself cause the GFCI to trip?


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## woodchuck2 (Sep 18, 2009)

don_resqcapt19 said:


> How would the bulb itself cause the GFCI to trip?


Honestly i do not know but the bulbs are the common denominator therefore is where i would start. If there are no visible problems then try a different brand bulb. I have seen where some bulbs buzz, check to be tight, swap them out for a different brand and the buzzing goes away. The buzzing bulb you can put elsewhere and works fine, put back in the fixture and it buzzes again.


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## davew (Feb 25, 2012)

DCooper said:


> Fan manufacturer recommends it, and one light is over the tub.


My choice in this situation: dead front GFI on the load side of that switch leg in an accessible (but aesthetically pleasing) spot.

I mean really, was it over 8' ?


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## don_resqcapt19 (Jul 18, 2010)

woodchuck2 said:


> Honestly i do not know but the bulbs are the common denominator therefore is where i would start. If there are no visible problems then try a different brand bulb. I have seen where some bulbs buzz, check to be tight, swap them out for a different brand and the buzzing goes away. The buzzing bulb you can put elsewhere and works fine, put back in the fixture and it buzzes again.


I see no way that changing out a two wire device like a bulb would make any difference to the GFCI. If it did I would be looking for a grounding to grounded conductor in the fixture that was opened by the mechanical forces of changing the bulb.


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## DCooper (Dec 6, 2011)

don_resqcapt19 said:


> I see no way that changing out a two wire device like a bulb would make any difference to the GFCI. If it did I would be looking for a grounding to grounded conductor in the fixture that was opened by the mechanical forces of changing the bulb.


Guys- To follow up on this. I grabbed a new 6" can and wired it with a switch at the panel. Same issue. The only thing I have not tried is direct wiring a socket with the same bulbs. Also, what are the odds you would have three cans with the same issue?


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## JohnR (Apr 12, 2010)

It would be pretty good if the problem was with the switch. Or, with the conductors going to the lights. I guess that the reason the leds work, is the load isn't large enough to trip the GFCI.


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## Big John (May 23, 2010)

I'm with Don, I think you have a high resistance connection. The more you load the circuit, the more you increase the voltage drop back on the neutral, the more current will flow on your high resistance connection via the equipment ground.

If you're feeling froggy, you could put a (fused) mA meter in line with the equipment ground and I bet money you'd read fault current.

-John


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## DCooper (Dec 6, 2011)

Big John said:


> I'm with Don, I think you have a high resistance connection. The more you load the circuit, the more you increase the voltage drop back on the neutral, the more current will flow on your high resistance connection via the equipment ground.
> 
> If you're feeling froggy, you could put a (fused) mA meter in line with the equipment ground and I bet money you'd read fault current.
> 
> -John


See Post #12. I eliminated the entire circuit. Same Problem. With Same bulbs.


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## Big John (May 23, 2010)

Have you tried this on a normal breaker? I'm tempted to say the lamps themselves might have an internal short, and you're actually going out on overcurrent?

I'd be pretty impressed if a lamp could cause a ground fault when screwed into a porcelain socket. I just don't see where the fault current path would come from.

-John


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## DCooper (Dec 6, 2011)

Big John said:


> Have you tried this on a normal breaker?
> 
> -John


Yes. It works fine.
According to the Square D rep in breaker support:
1. Try different bulbs - done.
2. We have never heard of it, but anything is possible. As we do not test bulbs here.



Due to similar thinking of others here I also completely re-wired the lights, with the same result until the bulbs were removed.


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## Big John (May 23, 2010)

I assume you grounded the test fixture you wired into the panel?

I'd megger the fixture with the lamp in it just to see what it looked like. That's mighty odd.

-John


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## don_resqcapt19 (Jul 18, 2010)

Someone is going to have to explain to me how a two wire load installed in a two wire device can cause a GFCI to trip. 
Have you megged the neutral to the frame of the fixture with it completely disconnected? I seem to recall there were some fixtures that because of the design of the can it was very easy to create a grounding to grounded fault.
When you connected the fixture directly to the beaker, did you connect the EGC?


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## DCooper (Dec 6, 2011)

"During the normal operation of a typical 2-wire circuit, the current returning to the power supply will be equal to the current leaving the power supply (except for some very small leakage). If the difference between the current leaving and returning through the current transformer of the GFCI protection device exceeds 5 mA (± 1 mA), the solid-state circuitry opens the switching contacts and de-energizes the circuit. The mA used above stands for one thousands of an amp, so 5 mA is equal to 5/1000th of an ampere." from http://www.mikeholt.com/mojonewsarchive/Safety-HTML/HTML/HowGFCIsWork1~20020102.htm

So, If I understand the above correctly- The lights could cause a current differential greater than 5/1000th of an amp, therefore tripping the GFI. I could see a $1 bulb having that much leakage.


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## Big John (May 23, 2010)

_DBCooper, _the problem is that that lamp is screwed into a porcelain socket. Porcelain is one of the best insulators we have, and I would expect that porcelain socket *not* to conduct even 5/1000's of an amp to ground.

If the lamp isn't touching any other grounded part, where is this 5/1000's of an amp flowing to?

That's the confusing part. Somewhere there must be a path that allows current to flow to ground, and I do not see how a lightbulb would be creating that path, no matter how cheap it is.

-John


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## Roger123 (Sep 23, 2007)

John, I agree with your logic if there is some current on the EGC. But a GFCI will open on an imbalance of current and if there is some "leakage" on one of the two conductors, phase & neutral this could cause the breaker to open.


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