Grounding a garbage disposal

March 29, 2019 8:25 PM

I'm installing a replacement garbage disposal and found that there is no ground wire running through the conduit to the disposal, just hot and neutral (white and black, no green). The disposal instructions want a ground.

This seemed bad, so I googled around and saw some suggestions for GFCI as an alternative. Lo and behold, there's a GFCI breaker in my circuit box for the disposal and dishwasher, so apparently someone in the past thought the same. Is that sufficient, or do I need to get an electrician out here to take a look and possibly run a ground to the disposal?

posted by Special Agent Dale Cooper to Home & Garden (7 answers total)

Best answer: I’m not a an electrician but I've seen them run a ground to the nearest cold water pipe, so it's not a huge concern either way but mixing electricity with a sink in any fashion means you should have a professional involved.
posted by bonobothegreat at 8:51 PM on March 29, 2019

Best answer: When you say conduit, do you mean EMT (rigid metal tubing) or flexible conduit? In general, in locales where rigid metal conduit is used, the conduit itself is the ground conductor. Flexible metal conduit (it looks like BX cable, but you fish your own wires though it) can also be used as a ground conductor but only for short runs. If the conduit is properly grounded on the other end and you are using the proper clamp to secure the conduit to the body of the disposal (and the part of the disposal where the clamp attaches is metal) you may be OK. If you're not confident about your abilities to assess this stuff, it's time for a pro.
posted by Larry David Syndrome at 9:08 PM on March 29, 2019 [1 favorite]

Do *NOT* connect the garbage disposal's ground wire to a water pipe unless a licensed and qualified electrician tells you to.

Depending on your house's plumbing and electrical system, doing so might be OK, or it might energize a section of your plumbing with line voltage in the event of a fault in the disposal. This could be dangerous/fatal.
posted by Juffo-Wup at 8:58 AM on March 30, 2019 [3 favorites]

To more directly answer your question, a GFCI in lieu of a safety ground connection can be acceptable in certain situations. I am not sure whether it would be acceptable (or safe) for a garbage disposal. I would probably prefer to err on the side of checking with an electrician.
posted by Juffo-Wup at 9:06 AM on March 30, 2019

Seconding Juffo-Wup, and noting that NEC requires all ground wires to connect to the actual ground (earth) at the main panel only. Doing otherwise can not only do what Juffo says, it can allow trickle currents in the pipe/ground, which can not only shock, but also cause metal pipe to deteriorate rapidly if it becomes an anode in the circuit. It can also cause the water heater to eat the sacrificial anode inside them rapidly.
I've seen all of the above in the field.
posted by rudd135 at 9:51 AM on March 30, 2019 [2 favorites]

Adding as a homeowner, the fact that the previous disposal was hooked up with no obvious ground COULD mean that there's something you're missing, but it could also more likely mean that some lucky idiot hooked up the last disposal.

Or that hooking it up to a water pipe as ground worked fine until the material of the plumbing changed.

Or that hooking it up through conduit-as-ground worked fine until somebody tweaked some wiring somewhere else and suddenly the conduit isn't grounded on the other end.

Or, or, or...if you're in any doubt, there are nice specialists with specialist tools & training who can remove doubt.
posted by ivan ivanych samovar at 6:37 PM on March 31, 2019 [1 favorite]

Response by poster: For posterity, the electrician came and checked it out--the flexi conduit attached to the unit itself acted as ground up to the switch box, so all was good and 100% up to code. Definitely good to have an expert verify it, though--thanks, everyone.
posted by Special Agent Dale Cooper at 8:50 PM on April 18, 2019 [2 favorites]