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I'm planning on putting an electrical box in my sink base with a split outlet, one for the dishwasher, the other for the garbage disposal. I was thinking of running 12/3 MC from the wall gangbox (metal box + metal cover with knockout) to another metal box in the sink base. Is this a legitimate / normal practice?

I've seen some solid plastic outdoor gangboxes that look like they'd be more appropriate under a sink but then I would have to run non-metallic cable.

Thanks

  • By "split outlet" do you mean a multi-wire branch circuit? Or is the other wire for the switched garbage disposal? – Harper - Reinstate Monica Aug 4 at 14:38
  • No MWBC, just the switched leg for the disposal. – DrTarr Aug 4 at 18:02
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I am assuming you are trying to install a switch leg for the disposal and a continuous hot for the dishwasher and the disposal and, dishwasher are on the same circuit, and you are trying to use a split duplex for both devices. I am also assuming that you are trying to surface mount the box inside the cabinet rather than use a cut-in box.

If you are installing a surface mounted box the conductors or cabling would have to protected no mater what kind of box you are using. If you came out of the side you would have to protect the conductors until you could pass into the interior of the wall or some other protected area.

One other problem exists the dishwasher circuit requires GFCI protection and the disposal doesn't. So if you do not have GFCI protection for this circuit you cannot put a split receptacle in under the cabinet. You would have to install two separate receptacles (at least one GFCI protected) or add a GFCI breaker to that circuit.

Taking this one step further. Since the NEC requires at least the dishwasher to be GFCI protected, it would be safe to assume that the area below the sink is considered by AHJ to be a wet location which would mean an "outdoor gang box" would be required in a surface mounted box.

FYI - The new 2020 NEC has modified 210.18 (A) which will require every 120V outlet to be GFCI protected including disposals, as well as any other wet location inside and outside a dwelling.

Hope this helps

  • All of your assumptions are correct. It was my plan to put both devices on a common GFCI, dishwasher included. It's possible I might ditch the plan for a GFCI breaker and instead do a GFCI receptacle (DW) and 2nd switched receptacle on the load side (GD). Regardless of either setup, is MC cable sufficient protection? If so, I'd need a metal outdoor box, would something like this be appropriate: lowes.com/pd/… Or is seal-tite necessary with this box? – DrTarr Aug 4 at 17:15
  • @DrTarr is PVC-jacketed MC available to you, or are you limited to unjacketed MC cable (where the metal armor is bare)? – ThreePhaseEel Aug 4 at 17:41
  • I can get PVC jacketed MC cable. I'd just need a fitting to go from MC to that outdoor box. – DrTarr Aug 4 at 18:05
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Given a choice, metal is always the way to go, unless it's impossible for some reason. Metal is both grounded and a good heat conductor, so it will do a much, much better job of containing a variety of wiring faults. It also has standard knock-outs, so you can attach anything instead of only Romex cables.

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The metal box and 12/3 MC is a normal installation. check to make sure you're not overloading the circuit you're tapping into? Those appliances usually have their own circuits.

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    This isn't going to be a MBWC, both outlets would be the same circuit, just one will be switched (wall switch for garbage disposal) and the other line voltage for my dishwasher. – DrTarr Aug 4 at 13:33
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Assuming you are under requirements of the NFPA National Electric Code (NEC):

A dishwasher and disposer are both motor driven, permanently connected appliances. Each requires a separate branch circuit. The location under the sink cabinet is not considered a wet location, and therefore does not require special boxes or covers.

You must mark

You may use NM (Romex) cable for both branch circuits.

Under NEC 2017 210.8(D), the dishwasher requires a GFCI. The disposer's installation instructions dictate the requirement for GFCI protection. Normally, a conventional duplex receptacle is used, with each receptacle separately powered from a GFCI breaker-protected branch circuit.

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