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Electrical Wiring

gfci outlet cycles on and off - does not trip

15 years ago

I have a 20A GFCI outlet outside on the front wall. This circuit supplies a 13W CF fixture atop a lamp pole (enclosed - not wet) and the 20A outlet itself. A low voltage transformer for LED yard lights & a 300W pond pump are plugged into this outlet. The power from the LOAD side as well as to the outlet itself cycles on and off in 10 min/5 min cycles as long as the pump (or anything else besides the low volatge transformer) is plugged into the outlet. If I unplug everything except the low voltage transformer (it is only around 12 watts) then everything works fine. The GFCI plug tests and resets as expected. The GFCI plug is only 3 years old. So, other than pulling a whole new circuit from the breaker box to the front of the house - what can I do to diagnose & remedy this problem?

Thanks

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Comments (5)

Billl
15 years ago
The GFCI circuitry measures the difference in current from the live to the neutral. If the difference exceeds a certain threshold, it trips. That threshold is very small, so pretty small problems can cause it to trip.
One possibility is that somewhere along the neutral, a wire is loose or corroded/oxidized. If a small current draw doesn't trip the GFCI but a larger one does, that would be where I would start. A bad connection somewhere could be sapping a couple milliamps, and that would be enough to trip it. It shouldn't take long to check all the connections since the circuit is so small. Take out the GFCI, clean up the terminals and the wire ends. Reinstall and make sure everything is tightened down well. Do the same for the light fixture.

Of course, another possibility is that the GFCI is faulty. They should last for many years, but a certain percentage of any product is going to fail prematurely.
Billl
15 years ago
Sorry -after rereading your post, I'm not sure I understand the symptom exactly. Are you measuring the voltage before the GFCI and noticing a drop or is the GFCI being reset after the power stops at the pump? Are you really seeing this at a fixed interval or just every few minutes? Did you change anything or has this basic setup worked properly for 3 years and is now just giving you a problem?

Also, does the power drop at the GFCI correspond to anything else in the house? eg Electric motors/compressors cycling on and off (like a fridge in the garage) can sometimes mess with GFCI's.
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The GFCI "stopped working" during the winter. You most likely mean that it no longer provided power. You shorted its wires and failed to trip a breaker. I'm going to bet that the original failure wasn't the GFCI itself, but in the wiring leading to it. If a non-contact tester shows voltage on both sides, I'm going to further make the guess that the neutral conductor is broken somewhere. Your two-wire tester will likely show voltage between hot and a known valid ground. ("known valid", in this case, means "not necessarily the ground wire in the gfci box.")
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I can almost guarantee that there are one of two problems: 1. The GFCI isn't getting power. 2. You have a ground fault. You're not going to find either one with just a night light. GFCI's often have other outlets connected to their protected side. If there's nothing plugged into the GFCI likely the problem is in the wiring beyond. Often water can get into outside boxes and cause such trips.
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The little outlet testers can't test GFCI without a ground. They leak a small amount of current from hot to ground which won't work without ground. As already suggested, the easiest and most effective way to test is use the TEST button on the GFCI. Randy: Actually to this day bathroom receptacles are allowed to be on circuits that serve only receptacles in one or more bathrooms. The other option is that a circuit may serve only outlets (receptacles and lighting, etc...) in a single bathroom. As Mike points out, adding GFCI's is cheap and easy if they are found to not be present.
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As Ron said, GFI breakers seldom fail. GFI receptacles are another story, they are notorious for failures. So it could be the GFI, but more likely the GFI is telling you that something is really wrong. Basic troubleshooting is in order. Ideally you'd measure the actual leakage current, but there's a simple if less accurate way. If the GFI never trip when nothing is plugged in, disconnect the charger from the extension cord and plug the cord into the outdoor receptacle. If the GFI trips with the cord plugged in but the charger disconnected, most likely it's the cable; replace it. A cable lying on the ground and/or in the sun for years will deteriorate and its insulation will fail. A much better and safer solution is to have a proper receptacle installed in the shed. If the cord alone doesn't cause tripping, plug in the charger. If the GFI now trips, have the charger serviced or replace it. A charger stored in a protected outdoor area can get all kinds of junk inside it -- cobwebs and mouse excreta and/or nests for example. These can get damp and cause leakage current. If a mouse mama raised her babies in there, you'll probably decide to junk the charger. Cleaning up mouse urine and the resulting corrosion ain't no fun, and could be a health hazard.
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pharkus
15 years ago
My understanding of the original post is that no "measurements", as such, have been taken at all - the poster simply notices that all of the devices downstream of the GFCI turn themselves off/on at a regular interval. The GFCI is not actually tripping - ie, no manual reset is necessary.

I did not reply initially as this seems like a very odd, difficult to explain problem.
Billl
15 years ago
That is odd. It almost sounds like the higher current is heating something up to the point of failure. Once it cools down enough, the power comes back on and it just keeps cycling on and off. Have you tried something with a big power draw (like a hair drier) to see if it fails faster than just the pump?

Unless you get better suggestions, I just start troubleshooting and ruling stuff out.

If the GFCI isn't tripping, that means you probably aren't losing any power from the outlet down. Otherwise, current "in" wouldn't equal current "out" and it would trip. To confirm that, you can just disconnect the line from the GFCI to the lamp and test the outlet again. If the problem still occurs, you know you don't need to worry about anything going out to the lamppost. That narrows the search area down to somewhere between the box and the GFCI. If the problem magically disappears, then you know it is in the run from the GFCI to the light.

If the problem sticks around, you have the connection at the box, a run of wire, a connection at the GFCI, and the GFCI itself as possible failure points. I'd rule out the connections first, then the GFCI, and save a new run of wire as the last resort.
btharmy
15 years ago
Check for loose connections at the GFCI. If, as you describe, the loss or cycling on and off only occurs when there is a heavy load the heat may cause the loose connection to heat up and break contact, after cooling off it shrinks making contact again and the cycle continues.

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