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loftezy 09-04-2009 09:48 AM

Sump Pump Electrical Problem
Over the past few weeks I've noticed that my sump pump in the basement is tripping the GFCI switch that it is plugged into. I've lived in this house for two years and the GFCI was installed when I moved in, so it is relatively new. I did some quick and simple diagnostics and this is what I found:

-The GFCI does NOT trip when I plug something different into the outlet.
-The GFCI trips when the sump pump is submerged in the sump basin even when the pump isn't pumping
- I pulled the pump out of the water, plugged it in, and it didn't trip.

So, in my amatuerish opinion, this tells me that water is getting to either the electrical parts on the pump or the wires. How should I proceed from here? Should I replace the GFCI anyways since it is a cheap first step? What usually fails on a sump pump that could cause an electrical problem?

I couldn't make out the manufacturer of the pump but the pump switch/float is a SJE Micromaster Plus.

Daniel Holzman 09-04-2009 10:06 AM

A GFCI is designed to trip when there is at least a 5 milliamp difference between the current flow as measured on the hot and the neutral. The design assumption is that the difference represents a current loss, presumably a ground fault, and at 120 volts 10 milliamps is apparently the maximum safe amount of current that can be passed through you without the potential for injury, so a device that trips at 5 milliamps is considered safe.

Therefore, if your GFCI is functioning correctly, and it appears that it is, the GFCI is sensing a leak to ground from your pump or the float switch. The fact that it occurs when the pump is wet suggests a small leak between the motor winding and the case. If the pump is dry, the case would be energized, but there would be no low resistance ground path for the current to flow through, and the GFCI would not trip. In the wet condition, the path to ground is lower resistance, and you are apparently getting more than 5 milliamps leakage.

You can check the GFCI by pushing the button on the GFCI, if it trips and resets normally, combined with the other tests you did, it is probably OK. You could always replace it, however if the replaced GFCI conditions to trip when the pump is wet, it indicates a fault in the pump, which would need to be replaced to be safe. As to why a pump goes bad, there is a lot of electric wire in a pump, if any of the energized wires get loose, or the insulation breaks down, or the seal goes bad, the wires can come into electrical contact with the case, which would cause the failure.

In most cases, there is no point repairing the pump, as the cost to repair for a small residential pump exceeds the cost to replace. By the way, for sump pump applications, I recommend a commercial grade pump with a cast iron casing, and solids handling capability. I have a Barnes 0.4HP, not that I am endorsing Barnes specifically, but mine has been in service since 1992 with no apparent problems.

It is possible that the float switch is bad, however this seems unlikely since if it were, you would trip the GFCI independently of actions of the pump.

loftezy 09-04-2009 10:21 AM

Thank you for the response. I'll pull the pump out and look for obvious signs of failure (cracked gaskets, cracked wire sheathing, etc) but I am resigning myself to the fact that I will probably have to just replace the pump.

I just have to find a place here in town that sells sump pumps - basements aren't too common here in California :)

Ranger31 09-06-2009 04:27 PM


There always mail order.

I buy a lot from a company call: GRAINGER Industry Supply

EBFD6 09-06-2009 06:09 PM


Originally Posted by Ranger31 (Post 324515)

There always mail order.

I buy a lot from a company call: GRAINGER Industry Supply

Grainger does business to business sales only. They do not sell retail, thus will not sell to home owners.

You could try Home Depot or Lowes they both sell sump pumps (around here anyway).

micromind 09-06-2009 06:14 PM

If you have no luck with Grainger, one other outfit I deal with a lot is MSC.

They have sump pumps, ship quickly, and will sell to anyone with a credit card.


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