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I have a GFI receptacle in the garage that protects the bathrooms and outside receptacles, everything is three pronged. Recently the circuit has been shutting off on a regular basis. I thought I had found the problem in the outside outlet where the face was cracked so I replaced the outlet this seemed to fix it for a while. No luck. Next I checked the fish pond pumps, air pump was not working, replaced it, No luck. Next checked the water circulation pump had a faulty cord with burned insulation at the plug between line and common blades, replaced pump, No Luck. Could all of these faults worn out the original GFI? It is 30 years old and came with the house when new. I read that GFIs don't like motors but the previous pump ran for two years before problems showed up. Should I get a higher amperage GFI or replace it with the same type?

  • What is the size of the breaker protecting this circuit? What is the gauge of the wire? Presumably these are copper wires--are they? What do you mean higher amperage gfi? Are there different current limits specified for GFCI receptacles? This would be for leakage current so this would be 5 mA, 10 mA, 20 mA . . . – Jim Stewart Jun 9 '17 at 12:33
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    I would immediately get a new GFCI receptacle and replace the 30-year-old one. This is "throwing parts at the problem" but the part is cheap and easy to install. Following a GFCI trip, does simply pushing the reset button immediately restore operation? I take it that this one circuit supplies more than one bathroom, a receptacle in the garage, and an outside receptacle, right? This is no longer allowed by code, but is probably grandfathered in your case. – Jim Stewart Jun 9 '17 at 13:13
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    If the arrangement permits, you might also separate these circuits to better isolate what's upsetting the GFCI. i.e. if the loads come off the GFCI and go multiple directions from that box (may or may not be true) put in a bigger box and another GFCI so some of the loads are on one, some on another. This would be a stop-gap on the road to perhaps eventually separating them all the way back to the breaker, but as noted, your installation is presumably grandfathered as is. And yes, GFCI's do fail from old age/use. – Ecnerwal Jun 9 '17 at 14:56
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    Your GFCI is most likely defective. Replace it - it is cheap enough you got your moneys worth at 30 years. I had one outdoors that had corroded terminals replaced it and no more problems. – Ken Jun 9 '17 at 21:19
  • Stewart,1a pushing the reset button immediately restores power if the pond pump is disconnected. 1b this gfi supplies power to three bathrooms, one garage plug and one outside plug – Russ Jun 10 '17 at 2:05
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It's true GFCI's do go bad and will wear out over multiple trips. So replacing one after 30 years is a good idea since the replacement is not all that expensive. But lets say the replacement does not fix the problem.

So to start, let's look at how a GFCI works. It is a closed loop system unlike an overcurrent protection. It actually measures the current in the hot wire against the return current in the neutral and if it senses a slight difference. It acknowledges there is leakage in the circuit itself. Since it is not intelligent it can only assume that there is a problem and therefore it trips.

When we troubleshoot a GFCI. WE start by removing all loads attached to the device. Then if we reset the device and check to see if trips. If it does not trip then one or more of the pieces of equipment attached to the circuit has some sort of problem. If it does trip we know that the installed GFCI device and its circuit is the problem and you begin a step by step approach to investigate and locate the problem internal to the circuit itself.

Moisture is a big player in GFCI tripping and you don't need much. For example many times on a construction site after a rain, an extension cord with a very small crack or cut in the jacket, not the insulation, will absorb enough moisture into the fill material of the cord to trip a GFCI. Remove the cord and set it out in the sun to dry for a few hours and you will be able to plug it back in and it will work.

So remove all equipment from the circuit. Check all cordage and exterior devices for moisture and make sure they are in good condition, clean and dry. Pay attention to equipment cordage that is making contact with the earth. More than likely the problem will make itself apparent. Reset the GFCI, if it stays reset then plug each piece of equipment onto the circuit one at a time and check to see which pieces of equipment are tripped your device. Replace or repair any piece of equipment causing a trip.

Hope this helps.

  • I got to this point by following your troubleshooting method and it is narrowed down to the pump. The pump is new and its cord is in good shape. I will repair the old pumps cable and return it to service to see if that stops the trippping of the circuit – Russ Jun 10 '17 at 2:23
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According to this* the trip current for a UL 943 Class A GFCI is 4 to 6 mA. If I were you, given all that is on this circuit, I would just install a new decent quality, residential grade 15-A GFCI receptacle. Even if the circuit is wired in 12 AWG copper and protected by a 20-A breaker, you can still put on a 15-A receptacle. *https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf

  • If I unplug the new water pump the gfi continues to previde power When I plug it in it trips the breaker. The pump draws 900 W. I will replace the GFI and try again. Thanks for all your help – Russ Jun 10 '17 at 1:57
  • If there is a specific appliance that causes the GFCI to trip, then you should focus on that appliance or its cord before changing the GFCI receptacle. This is new information! This indicates that the water pump or its cordage has a ground fault. A new GFCI receptacle would probably trip also. It would appear that the new water pump actually has a ground fault or the power lines or receptacle through which it is connected has a ground fault. How is the water pump connected? – Jim Stewart Jun 10 '17 at 10:10

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