GFCI trips when switched on...SOMETIMES

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  #1  
Old 10-23-07, 08:08 PM
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GFCI trips when switched on...SOMETIMES

I have installed a pair of exterior outlets to power a small pond pump on one circuit, and low voltage landscape lighting on another. (300A Each circuit has a switch, and controls a seperate GFCI.

My problem is that SOMETIMES, turning on the circuit with the lighting trips the GFCI on that circuit. I know it's not being overloaded, as I took off almost all of the lights and it still happens. I even tried switching the sources, by putting the lighting on the circuit that the pond pump was on. Same results, the lighting circuit GFCI is tripped. It has never happened on the pond pump circuit, and only happens about 85% of the time on the lighting circuit.

I have included a diagram of how I have it wired. The junction box is used to connect interior/exterior wires. I'm not sure about sourcing both GFCI circuits from one



The pond pump is a very small pump purchased from Home Depot, and the landscape lighting is from a DIY box:
http://www.homedepot.com/webapp/wcs/...egoryID=502497

Am I doing anything wrong or could it be the transformer going bad???
 
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Old 10-23-07, 08:30 PM
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There should not be a problem with the way that you wired your switch legs.
GFIs do not trip on overload, they trip when an imbalance is detected on the hot and neutral.
If both GFIs have tripped when you plugged in the lights, then obviously you have a lighting problem that you need to isolate.
Rather than removing all the fixtures, start with just disconnecting the wire from the xformer to the lights and see if you can replicate the problem.
If it still trips, you have a bad transformer which I am going to bet is the case.
I would doubt that the low voltage side is causing the tripping but it might be worth checking the connections on the light fixtures.
 
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Old 10-24-07, 04:08 AM
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If these are not relatively new GFCIs then you may want to replace them. In recent years the technology has gotten better at reducing nuisance trips.
 
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Old 10-24-07, 08:56 AM
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Thanks, everything is new including the GFCI's, transformer and lights. Relatively new I guess, about 2 months old. It worked fine before, recently started this problem so I was leaning towards a bad transformer too. I will try removing the low voltage wiring from the transformer and see if that does it.
 
  #5  
Old 10-24-07, 12:38 PM
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no luck

I replaced the transformer with a new one, same issue. I turn on the switch, reset the GFI and plug in the lights. They come on as normal, I can even un-plug and plug back in many times and the GFI will still not trip. I turn the switch off, the GFI still stays engaged...but when I turn the switch back on. pop.

Does the fact that I can plug in/out the lights without problem point to the switches??

Thanks in advance for your help
 
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Old 10-24-07, 01:19 PM
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I would place a single GFCI somewhere between the breaker panel and the switch and eliminate the ones at the plugs themselves. I think the problem might be a combination of in-rush current and switch bounce. Since the GFCI is not powered itself until you turn on the switch, any compensation circuitry built into it is inactive for a few nanoseconds after you turn it on. Enough time to make it useless in this case.

Moving the GFCI would also provide desirable GFCI protection for the wiring that is buried in the yard...

Doug M.
 
  #7  
Old 10-24-07, 08:31 PM
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Thanks, that's a good idea and not too expensive. Is it common practice to keep GFCI outlets powered at all times because of that issue?
 
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Old 10-25-07, 07:21 AM
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I'm not sure too many people think much about keeping a GFCI powered because of its circuitry, but I'd say it's somewhat unusual to find one that's switched simply because most places where a GFCI is required wouldn't need to be. The closer it is to the source of power, the more it will protect.

Doug M.
 
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Old 10-25-07, 07:30 AM
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Yours is not a commonly reported problem, but having a switched GFCI is not very common either. I have no idea why your problem exists, but Doug's suggestion will probably avoid it. Be sure to replace the exterior GFCIs with ordinary receptacles when you put the GFCI upstream of the switches.
 
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