garbage disposals and GFCI

February 25, 2006 3:36 PM

My garbage disposal trips the nearby GFCI circuit every time I use it. What can I do?

We've been in our house about a year and a half. Starting about a month ago, every time I flip the wall switch to turn on the in-sink garbage disposal, the nearby GFCI outlet switches off within a second or two. The disposal is plugged into an outlet under the sink, which is not GFCI, though I assume it’s on the same circuit.

If I plug the disposal into another outlet on a different circuit, there’s no problem, though, of course, this isn’t really practical. If I plug something else into the under-sink outlet, also no problem.

I tried the easy fixes first. I changed out the wall switch and the GFCI outlet, to no avail. I haven’t tried changing the under-sink outlet yet, because it’s hard to get to. Plus, I sort of doubt it’ll have any effect.

What to do? I’m guessing there’s a problem with the disposal itself. I’m pretty handy, so I could take it out, if need be, but, of course, I’d rather hear about any possible easy solutions to try first.

posted by MrMoonPie to home & garden (10 comments total)

I think what this means is that current is flowing in the ground wire of the circuit instead of the neutral/return wire where it is supposed to be. This is a safety issue, as it can mean that the metal casing of the disposal might have shorted to one of the wires. So I suppose you could take it apart and look for any obvious signs of the casing impinging on any wires. If that fails though I wouldn't hesitate to call in someone that knows what they're doing, since you're talking about your safety here. Would it really be worth eletrocuting yourself while washing dishes because you wanted to save $75?
posted by Rhomboid at 4:33 PM on February 25, 2006

You've got a current leak to ground. Considering disposals are less than $200 I'd just replace it with a new one.
posted by Mitheral at 4:44 PM on February 25, 2006

Do you have a multimeter? (probably you should get a cheap one if you don't already have one anyway) Unplug the disposal and try measuring the resistance between the two power prongs of the disposals plug and the round ground connector. If you get any resistance less than tens of megaohms, the disposal is bad. While you are at it, you should make sure there is very little resistance between the ground of the plug and a unpainted part of enclosure of disposal.

I'd also take one of those handy outlet diagnostic plugs, the ones with the three lights, and make sure the outlet is wired correctly.

Finally, since you are already under the sink, I'd make sure there is very little voltage, and little resistance, across the ground connector of the outlet and the water pipes. If there is, you may have a serious problem.
posted by darkness at 4:46 PM on February 25, 2006

Before replacing it, plug a lamp into the under sink outlet and see if that trips the GFCI (In fact, maybe try your vacuum too, that way, you have tried a range of different loads).

I guess it probably is the disposal, Mitheral is usually right about these things :P
posted by Chuckles at 4:55 PM on February 25, 2006

On second thought there one easy thing to check and one easy repair to attempt. The easy check is to plug your disposal into a three prong extension and then plug it directly into your GFCI. If the extension corded disposal doesn't trip your GFCI then you have probably have a dirty/defective under counter outlet, the current leak is across the face of the outlet. I've seen this once in a laundry room.

The simple repair addresses an unlikely but possible defective power cord. You could try wiring a new cord and plug onto the disposal. Cheap source for the cord and a moulded plug is an all weather extension cord.

Usually though when this happens the shaft seal in the unit is starting to leak. Water drips down into the motor and trips the GFCI.

The reason it is tripping your counter GFCI outlet is a counter outlet adds GFCI protection to the everything downstream (but not anything upstream). This by the way allows a cheap way to add GFCI protection to an entire curcuit with out having to buy an expensive GFCI breaker (some 15A GFCI breakers are $100 wholesale). Just install a GFCI outlet as the first outlet on your curcuit.

PS: if this is a 18 month old home your disposal may be under warranty, many of them have two years parts and labour.
posted by Mitheral at 7:45 PM on February 25, 2006

Awesome. It's late now, but I'll check out some possible solutions tomorrow. Thanks, all! AxMe freakin' RAWKS!
posted by MrMoonPie at 8:06 PM on February 25, 2006

Okey doke, tried plugging the unit directly into the GFCI, and the circuit tripped. I'll be heading to the Home Depot to get a sacrificial cord next.

If that doesn't work, though, can anyone give me guidance about brands/models of disposals to get? On the Home Depot website I see Maytag and In-Sink-Erator, 1/3 to 1 horsepower, $58 to $299.
posted by MrMoonPie at 9:27 AM on February 26, 2006

I recently got the in-sink-erator 555ss from home depot for about $170. Consumer reports had rated it 2nd from the top, just below a $420 Viking model. Unfortunately, I'm still waiting for the kitchen plumbing to be completed, so I haven't had a chance to try it out yet.

Oh, and BTW, you don't need to get a "sacrificial cord" to wire a new cord up (I take this to mean you intend to buy an extension cord, cut the end off and wire it up), they sell cords with the ends already cut off and wires stripped in the electrical section next to all the other extension cords.
posted by darkness at 12:25 PM on February 26, 2006

The new disposal is installed, and it no longer trips the circuit. Yay!

I pulled the old disposal, intending to try changing the cord. But the unit was old and decrepit looking, so I just went and bought a new In-Sink-Erator Badger 1 for $58. Took about 45 minutes to install, and it works great.

(as an aside, we're figuring out that lots of stuff in our "new" house is obviously salvaged. The guy who did the renovation was a semi-pro do-it-yourselfer type, and did a half-assed job wherever he felt he could get away with it. So while he installed the disposal 18 months ago, it's likely much older.)
posted by MrMoonPie at 3:19 PM on February 26, 2006

darkness writes "Oh, and BTW, you don't need to get a 'sacrificial cord' to wire a new cord up (I take this to mean you intend to buy an extension cord, cut the end off and wire it up), they sell cords with the ends already cut off and wires stripped in the electrical section next to all the other extension cords."

Yep, but you can often buy a 15m 16GA extension cord for the same price (or cheaper) than a 3m 18GA cord with only the plug. And you get 15m of wire with better casing instead of 3m.
posted by Mitheral at 5:29 PM on February 26, 2006