Testing a GFCI

[Tom7227]

My sump pump keeps tripping the GFCI. When I plug the pump into a non protected circuit it works fine. Is there a way to test the pump to see if that is the problem? The GFCI works when I use a plug in tester and it also shows that the unit is properly wired.

Thanks for your time.

Tom

[delcecchi]

Unplug the pump. Use digital multimeter on "ohms" to measure the resistance from hot to ground and neutral to ground in the plug. I think they both should be very high, like 100k or more. Leakage current in the pump will trigger the GFI. It doesn't take much (around 5 ma) which would be a resistance of 20k or so.

Some water could have gotten into the wiring or there could be a little corrosion that is causing leakage. Anyway, the GFCI is probably doing just what it is supposed to do, stopping current from taking a stray path to ground, like it would in an accidental contact.

A GFI works by comparing the current in the hot wire to the return current in the neutral. If they are different it shuts the juice off because something is going somewhere it shouldn't.

[Tom7227]

Del,

Thanks for the info. I checked and I am getting a reading on one side and a reading of 125 or so on the other when the pump and the float valve are bot connected. I get equal readings when testing the pump alone and no reading at all testing the float valve alone. Does the float valve have to be activated to be able to get a proper test? It is a ball type float valve, not the one that slides up and down a shaft.

Thanks again.

Tom

[delcecchi]

Since you are looking for leakage to ground, I would try all possibilities. The switch is, I think, connected between the hot wire and the motor, in series, although I haven't verified that.

So in terms of leakage to ground, if the pump is unplugged there shouldn't be any whatever the position of the switch. I would try both ways to be sure.

If you are seeing 125 ohms and not 125k that would be a problem indicating a lot of leakage. 125k would only be 1 milliamp which isn't enough to trigger the gfi.

[CAMAN]

From everything i have read motors should never be plugged into GFCI outlets.

[Tom7227]

Typing was bad - I rechecked and I am getting readings of about 256 ohms on both sides of the plug for the motor. I get zero on the plug for the float valve both when it is plugged into the motor plug and when testing it alone. The setup still works properly when plugged into a non-GFCI protected outlet.

I suspect this means that the float is bad.

I thought I was told that you have to have a GFCI wherever there is water within a few feet of an outlet. I will be happy to remove it if that is not required by code.

[delcecchi]

I checked one of mine. the reading from either side of the plug to the ground prong was infinite, more or less. No reading even on the 20k scale. Switch on or off made no difference. If you are seeing conduction from hot or neutral to ground under any circumstance I think the motor or switch is bad.

256 ohms to ground!!! Sounds like something got full of water.

[low277]

Del is right about the GFCI measuring the current flow on the hot and neutral wires. If they are not within about 5ma of each other it trips.

I believe that there used to be a exception to the code (NEC 218.8)that allowed a sump pump on a non GFCI protected circuit if it was plugged into a single receptacle but I think that exception was deleted a couple of code cycles ago.

There is something wrong with either the pump system or the GFCI, I would not take the GFCI out of the system, either replace it with a new one or repair/replace the pump system.

[Tom7227]

I went to the Oakdale Fleet Farm and got a new float valve and will give it a try. I was surprised to see that they still had a fairly decent number of pumps on the shelf and staff was putting more out.

[JohnMickish]

Here is my take on this, and the industries take as well. Electric motors WILL have nuisance tripping of a GFCI. It is because of the nature of the GFCI and how it measures the difference in current between the hot and neutral wires. It thinks that if the current is not the same that YOU are being electrocuted and it will open itself to save human life. That is what it was built for.

When an electric motor is first turned on there is induced magnetism and all sorts of things going on for the first few milliseconds. In these first few milliseconds the current flow between the hot and neutral wire are not the same. A GFCI will open if it sees an imbalance within the first 7 sine waves.

There are a few things you can do to help yourself.

First, is DO NOT use an extension cord.

Second, if you want to leave your sump pump plugged in all the time without a GFCI, install a single receptacle (not a duplex, but a single) by the sump. By using a single receptacle and keeping the sump plugged in all the time you bypass the codes GFCI requirement since that receptacle is for a single in place piece of equipment. Put a duplex receptacle in there and it has to be a GFCI.

Hope that helps.

Oh, some GFCIs are "looser" that others and are more prone to tripping than others are, but it's a bad idea to plug important stuff like refrigerators, freezers and sump pumps into GFCIs.

[delcecchi]

Interesting. I have had a sump pump plugged into a gfci for years. This spring the gfci decided that it would trip once in a while, maybe once a day. I measured for leakage and found none. So I guess the GFCI has gotten more picky. I will try another one, and if that doesn't do it, go with the single outlet deal.

[JohnMickish]

GFCIs can be funny. I recently had 3 at work die within the first 12 hours of installation. These where not the Home Depot quality either, but Hubbell spec grade. Replaced them and they have been holding up fine since.

[low277]

I have been out of the residential side of the industry for over a dozen years. does the exception for the sump pump on a single receptacle still stand? I thought they mentioned at a continuing ed class that they had removed that exception?

[StillwaterAaron]

If you are still having issues with the GFCI replace it with a regular outlet. Sump pumps are not recommended to be plugged into GFCI outlets.

The other areas GFCI outlets are used is garbage disposal and garage door opener and both those are not supposed to have GFCI outlets.

[low277]

In an existing house, a homeowner can pretty much do as he pleases, although I think that the current NEC code would prohibit you from not having a GFCI.

It is at the point where if you are dealing with a dwelling and 115 volt receptacles that they will either be AFCI or GFCI protected, I think that there is a exception for a fire/smoke alarm circuit.

Can anyone confirm either way?

[JohnMickish]

Low, the last time I was in that section it was still there. Of course they added the whole finished/unfinished basement deal too. If the basement is finished you do not need to GFCI protect everything, only what is required, which would be bathrooms, wet bars, kitchens etc.

FWIW, it's been 5 code changes since I roped a house.