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Our garbage disposal trips its breaker when the unit is turned off. Flip the breaker and the unit runs, turn the unit off and the breaker trips. I have replied the switch. Wiring of the switch, double checked, is correct. Black wires connected to switch. White wires to other connector and white wires to the green screw on the switch. Any ideas on what may be wrong? Thanks!

  • Is it a GFCI breaker. Also, when you said "white wires to the green screw on the switch.". Did you mean green wires, or are there actually white wires connected to the green grounding screw? – Tester101 Oct 22 '15 at 23:18
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Are you in the USA? The green screw should be Ground (green or bare wire), not Neutral (white).

Generally:

  • Line is "hot", with the active AC voltage present.
  • Neutral is the return path for the current. All current should travel from Line, through the load, and then back through Neutral.
  • Ground is there for safety only. It should only carry current in the case of a fault.

In a standard circuit there is no indication that current is flowing through ground, as long as it's not enough to trip a breaker. However, your garbage disposal unit is connected to a GFCI breaker. This kind of breaker is specifically designed to open up when there is ground current.

It sounds like your circuit's Neutral is tied to the junction box. The junction box is also likely grounded. This ground connection is generally made by a bare copper wire attached to the back of the junction box.

At the same time, your disposal has a big motor in it. When you turn off a motor it creates its own current for a small amount of time as it spins down. Since this current can't return through the switch , it returns through ground. This trips your GFCI.

  1. First, verify the wiring connections. It is possible that the ground was wired correctly, but that someone did it with white wire (instead of green or bare wire) just to confuse everybody. Ideally, there should be one connection from the green screw to the junction box, and a totally separate connection between the white wire from the breaker box and the white wire to the disposal unit.

  2. If, in fact, all the white wires are tied together then you should disconnect your white wire from the green screw. Then run a wire from this screw to the grounded junction box.

  • The OP did not specify if the breaker was a GFCI device. If it is a GFCI, and the grounded (neutral) is tied to ground, and the receptacle ground is grounded. The GFCI should trip when the disposal is running, because some of the current will return through the grounding conductor. – Tester101 Oct 23 '15 at 2:47
  • @Tester101 True, I was assuming that he was in the USA and that the unit was on a GFCI for code reasons. If this isn't true then my answer isn't valid... – bitsmack Oct 23 '15 at 4:44
  • @Tester101 As far as my reasoning; I'm further assuming that his/her neutral wiring is very good but the switch body isn't grounded all that well. It's only held to the (presumably) grounded j-box with screws, perhaps with paint or drywall mud in between... If so, then the operating current would take the easier N path, but the inductive kick (with the switch open) could force through the poor connection to ground. I could be wrong! But even if this isn't the OP's problem, any N connection to ground should be corrected. Or am I missing something? Thanks! – bitsmack Oct 23 '15 at 4:47
  • Yes, if there's a neutral connected to ground, that should definitely be corrected. – Tester101 Oct 23 '15 at 12:23

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