Crazy GFCI stuff going on

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pete1980

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Hello,

This is my first post. I'm stumped. One of the branch circuits for my basement has 2 loads a sump pump on a single receptacle and a waste pump on a GFCI.
The sump pump is on a single receptacle and the waste pump is on a GFCI they are not connected in any way.

Sometimes when the sump pump kicks on it causes the GFCI to trip and I have to reset it. Why is the sump pump, which is on its own separate single receptacle outlet and not related to the GFCI in any way, causing the GFCI to trip?

Can someone explain to me what is going on here?

Thanks
Pete
 
LIM said:
They are on the same branch circuit but not related in any way?
Click to expand...

They are not connected. The one receptacle is not a load of the GFCI. The only thing they have in common is they share the same breaker.
I suppose I could replaced the GFCI to see if that resolves the issue but I would like to know why and how this is happening.
 
Since you and I are not electricians, we are not allowed to use this forum to help us perform our own electrical troubleshooting, repair, or installation. So please keep this discussion focused on the physics of the situation, and not on the possible solutions or corrective measures.

I infer that after the GFCI has tripped, the sump pump continues to function properly. Is that right? That would confirm that the simplex receptacle is not installed on the load side of the GFCI.

I drew a sketch to help me understand the situation. The only guess I can make (and it is admittedly a very long shot) is that there is a leakage path in both pumps. It would have to be of a high enough resistance that would not cause the breaker to trip on overcurrent. On the waste pump, it would also have to be of high enough resistance that would not cause the GFCI to trip from the normal operation of the waste pump. Since each pump motor has an EGC connected to its outer case, a leakage current (from hot conductor to case) internal to the sump pump would cause some current to flow along the EGC to the panel?s N-G bond point. Here again, the overall resistance of the leakage path has to be high enough for that not to trip the breaker. But some of that leakage current will also flow along the EGC to the case of the waste pump, then along the leakage path that is internal to the waste pump, then along the neutral wire leading away from the waste pump. That will be seen by the GFCI device as a difference in current between the hot conductor and the neutral conductor. That could be the source of the problem. This is more than a bit off the wall, but I can?t think of any other explanation. So I would now defer to Sherlock Holmes (?If the impossible is eliminated, then whatever else remains, however unlikely, must be the truth?).

One way to test this theory would be to plug the sump pump into the GFCI receptacle, and see if it causes a trip.

Regarding the role of engineers on this forum, I can say without hesitation that I have learned a great deal during the decade or more that I have been a participant.

 
With some GFCI receptacles (and even breakers) a surge or arc on the line side of the GFCI can still cause a trip, as can a surge on the load side that does not actually involve any stray current.
When this is suspected, a first step, or possibly after the tests charlie suggested, is to try a different brand GFCI.
 
Thanks everyone.

Yes the sump pump keeps working after it trips the GFCI.
I like your theory. I will plug the sewage pump somwhere else temporarily and put the sump pump on the GFCI to see what happens.
 
pete1980 said:
They are not connected. The one receptacle is not a load of the GFCI. The only thing they have in common is they share the same breaker.
I suppose I could replaced the GFCI to see if that resolves the issue but I would like to know why and how this is happening.
Click to expand...

Enough said?
 
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