How to Replace a Garbage Disposal – Part 4

How to Replace a Garbage Disposal – wiring a 120VAC electrical outlet under the kitchen sink.

This project is continued from Part 3.

The Waste King® Legend L-8000 garbage disposer has a plug in electrical cord, however my old disposal unit was the hardwired type. I therefore needed to install an electrical outlet under the sink to plug in the new Waste King disposer. Converting a hardwired electrical connection to an plug-in wall outlet is simple and inexpensive. I prefer a plug-in disposer because it’s easy to remove for maintenance and easier access to the sink plumbing.

Under Sink Electrical Outlet

I purchased a Leviton single outlet, steel outlet box and cover plate for $5.29 w/o tax at my local home improvement store.

Electrical Outlet and Box for Garbage Disposer

Electrical Outlet and Box for Garbage Disposer

I bought a single outlet to prevent any other appliance from being plugged to prevent overloading the circuit.

Electrical Safety

For safety’s sake, let’s review where I am in this project:

  • The garbage disposer is on a dedicated circuit from the main electrical service panel.
  • The electricity has been shut off at the circuit breaker in the main panel.
  • I verified there is no voltage on the house electrical wiring.

My garbage disposal is operated by an on/off switch located above the kitchen sink. Simply turning off the sink switch is not an adequate safety precaution.

Garbage Disposal Electrical Outlet Wiring

Since I already had the hardwired NM 12/2 electrical wire and flexible metallic conduit, installing the electrical outlet was easy.

  • Remove a prepunched knock-out from the steel outlet box by bending it in with a screwdriver and working the disc back and forth until it breaks off at the tab. I chose the knockout at the box end as the most direct way to bring in the wires.
  • Straighten the NM 12/2 electrical wires as shown in the photo below.
  • Remove the lock nut from the strain relief fitting.
  • Feed the wires and threaded end of the fitting through the knockout hole in the box.
  • Slide the lock nut over the wires and screw the nut onto the fitting as shown.
  • Tighten the lock nut by 1/4 turn – a flat screwdriver tip levered against a spur of the lock nut works well.
Kitchen Sink Electrical Outlet Box: Flexible Metal Conduit and Strain Relief Fitting

Kitchen Sink Electrical Outlet Box: Flexible Metal Conduit and Strain Relief Fitting

I purchased a Leviton single outlet rated for 15AMPs and 125VAC for $2.99 and backwired the outlet per the instructions printed on the package. I also scraped off the light coating of oxidation off the wire ends with a edge of the needle nose pliers to expose the shiny copper surface for a solid electrical connection before wiring the outlet. The three connections are: black wire (hot), white wire (neutral) and ground wire (bare).

Garbage Disposer Kitchen Sink Outlet: Backwiring Connections

Garbage Disposer Kitchen Sink Outlet: Backwiring Connections

Another view of the pre-wired outlet.

Garbage Disposal Under Sink Electrical Outlet Wiring

Garbage Disposal Under Sink Electrical Outlet Wiring

Note that I wired the outlet before mounting it on the wall at the back of the sink cabinet. Doing it know meant I could sit in comfort on the kitchen floor with the outlet lying in my lap instead of lying down and straining to reach the back of the cabinet!

Mounting the Garbage Disposer Outlet Box

  • Locate a convenient spot on the back of the sink cabinet for the electrical out.
  • Now verify the garbage disposal cord is long enough to easily reach that spot!
  • Mark a plumb line (vertical line) on the back wall of the sink cabinet with a carpenter’s level.
  • Hold the outlet against the wall over the plumb line.
  • Move the outlet so you can see the plumb through two of the screw holes on the back of the box.
  • Mark the center of the screw holes on the plumb line.
  • Insert two drywall anchors. I really like these self-drilling heavy-duty metal EZ Anchors that hold up to 50lbs.

If you can locate a wood stud behind the drywall to drive in the screws, then you can omit the drywall anchors. It was a long reach lying on my side under the sink to reach the back of the cabinet, so I used the drywall anchors for convenience.

Plumb Line and Drywall Anchors for the Kitchen Sink Outlet

Plumb Line and Drywall Anchors for the Kitchen Sink Outlet

Fasten the box to the wall / drywall anchors with two screws as shown below. You can see why I pre-wired the outlet before mounting the electrical box as it would’ve been very difficult to do wire it while laying under the sink inside the cabinet.

Under Sink Garbage Disposal Outlet Mounted to the Drywall

Under Sink Garbage Disposal Outlet Mounted to the Drywall

Verify the Electrical Wiring Connections

I turned on the circuit breaker and flipped on the switch by the sink to power the new receptacle. I plugged in a 3-wire receptacle tester to check for improper wiring such as reversed wires and open connections. These are really easy to use, just plug it in an confirm the light pattern with the reference chart. The two yellow lights means it’s wired correctly.

Under Kitchen Sink Outlet: Receptacle Tester

Under Kitchen Sink Outlet: Receptacle Tester

I flipped the garbage disposer switch by the sink to the off position and attached the steel cover plate to the outlet box. The new outlet is ready for service!

New Under Sink Garbage Disposer Electrical Outlet

New Under Sink Garbage Disposer Electrical Outlet

Garbage Disposer Electrical Outlet Installation Tips

Some tips when installing the garbage disposer electrical outlet:

  • Mount the outlet several inches higher than the bottom of the garbage disposer.
    This so water can’t run along the power cord and into the receptacle if you have a leak.
  • Route the wiring into the top of the box as shown above.
    Again, so leaking water can’t run along the flexible conduit into the box.

This project is concluded in Part 5.

Take care,

Bob Jackson

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12 Responses to How to Replace a Garbage Disposal – Part 4

  1. Steve Eppley August 24, 2011 at 2:46 pm #

    This guide has been extremely useful during my replacement of a leaky Badger 5 with a new Waste King 3300. I have a comment and three questions:

    Comment: If the sink is stainless steel, then putty isn’t needed under the sink flange, according to the Waste King instructions. A thin flat rubber gasket supplied with the disposal is used instead of putty. This makes the job even quicker and easier, one more reason to replace the Badger’s 3-bolt mounting hardware with the Waste King EZ Mount system. (Hopefully the rubber gasket will be at least as durable as new putty would be.)

    Question 1: Is there a way to install the drywall anchors for the power outlet box using only one hand? Underneath my sink there isn’t enough room to reach the wall with both hands. I bought self-threading anchors, but perhaps I should have bought the kind that need a hole drilled since a drill can be operated with one hand.

    Question 2: If the trap, waste arm and slip nuts are chrome-plated brass or galvanized steel, not PVC, will a sealant be needed and will a different kind of washer be needed? I tried using no sealant and the old gaskets, which aren’t tapered like the gaskets in your photos. The slip nut that connects the trap to the waste arm elbow must leak a bit, since it feels wet. So I need to buy some sealant and/or new gaskets, or replace the trap with a PVC trap. If I replace the trap, would a sealant be needed to make a watertight connection between the PVC trap and the metal elbow at the end of the waste arm? (My trap appears to be chrome-plated brass. The waste arm and elbow might be galvanized iron; they’re a dull gray and the elbow is threaded directly onto the waste arm with no slip nut. The building–8 stories of condos in Montgomery County, MD–was constructed in the mid-1970s, I think.)

    Question 3: Is the Permaflow No-Clog Trap a good product?

    Best wishes,
    Steve

    • Bob Jackson August 24, 2011 at 6:06 pm #

      > Question 1: Is there a way to install the drywall anchors for the power outlet box using only one hand?
      Try laying on your back with your head under the sink. Drill a small pilot hole in the drywall to insert the tip of the self-drilling drywall anchor, jab the anchor in the pilot hole so it won’t fall out, then drive it the rest of way in with the cordless drill/driver. Result: three one handed operations. A few grunts and ughs will get it done.

      > Question 2: If the trap, waste arm and slip nuts are chrome-plated brass or galvanized
      > steel, not PVC, will a sealant be needed and will a different kind of washer be needed?
      No sealant, however a plastic slip washer or rubber washer is required, the type depends on the manufacturer of your p-trap, arm and tee. Use the same style as the original part, or buy a whole new trap, arm or tee if necessary to get the right washers. Metal on metal without a washer will leak. Take your old drain parts to the home improvement store and compare what matches with a new item.

      > If I replace the trap, would a sealant be needed to make a watertight connection between
      > the PVC trap and the metal elbow at the end of the waste arm?
      Do not use sealant (glue, putty, etc.), a slip joint adapter will work.

      > Question 3: Is the Permaflow No-Clog Trap a good product?
      I not tried that product. It looks interesting and I can see the benefit of turning the knob to sweep up heavy sediment in the bottom of the trap. Questions that come to my mind are:
      * Will the see-through pipe become opaque over time as a thin film of dirt builds up inside the pipe?
      * It’s simple to disassemble a P-trap for cleaning.

      Give Permaflow a try and post back with your thoughts!

  2. Norms September 3, 2012 at 3:04 pm #

    Would it better to install a GFCI outlet? I believe my village electrical requires such setup (I still have to verify it though).

    Thanks.

    • Bob Jackson September 4, 2012 at 6:56 am #

      A GFCI outlet would be difficult to access to reach the Reset & Test buttons under the kitchen sink. Specialty single receptacle GFCI outlets may be available, but I’ve only seen duplex GFCI outlets. Since the 1HP Waste King Legend 8000 draws 7 AMPS and it’s best to place it on a dedicated circuit. Otherwise someone is likely to plug in the dishwasher, hot water dispenser or something else into a duplex GFCI and trip the circuit breaker.

      Instead of installing a GFCI duplex outlet under the kitchen sink, a much better solution is to install a GFCI circuit breaker in the main electrical panel. I did this for the instant hot water dispenser.

      You can easily replace a standard circuit breaker with a GFCI circuit breaker for the branch circuit serving your garbage disposal.

  3. Andrew November 6, 2012 at 7:01 am #

    Do you have to install an outlet? I was under the impression that I could directly wire my unit into my electrical.

    • Bob Jackson November 6, 2012 at 5:47 pm #

      An outlet is not required and you can direct wire the disposal as was the case with my old garbage disposal unit. I prefer a disposal with a cord & plug, therefore I needed to install an electrical outlet.

  4. Teresa Bennett February 8, 2014 at 4:26 pm #

    I am also replacing a hard wired disposal with a plug in. When we had the first disposal installed in this house (there wasn’t one previously) the electricians came off an exsisting outet, installed an on/off switch, then ran a white wire thru the wall, under the sink and attached it to the disposal. All the pictures I see of wiring for disposals show a metal clad wire. My intention was to install an outlet just as you’ve done in the article above. However, now I’m concerned that my wiring is incorrect to begin with. Any thoughts on this? I believe the wire is 14 AWG 15 amp with a white jacket.

    • Bob Jackson February 9, 2014 at 11:17 am #

      Your garbage disposal wiring is a common configuration although protecting the exposed NM-B 14/2 cable (the “white jacket” you described) with 3/8″ or 1/2″ aluminum flex conduit is a best practice.

      To install the aluminum flex conduit over the NM-B 14/2 cable:
      * Turn off the circuit breaker and verify the electricity is shutoff.
      * Disconnect the wiring from the garbage disposal.
      * Measure and cut the needed length of flex conduit.
      * Install an flex anti-short bushing in the end of the conduit where it will meet the NM-B cable coming out of the wall.
      * Insert the NM-B 14/2 white jacketed cable in the flex conduit. It’ll be easier if the cable is straight. 3/8 inch diameter conduit is a little snug where 1/2 inch conduit is has more room. Just be sure to use the same size fittings and bushing (3/8 or 1/2 inch). For the 2 or 3 feet of cable you probably have, I’d stick with 3/8 inch.
      * Wire the new outlet as shown in the project.

      The end of the aluminum flex conduit will simply meet the wall under the sink. The flex conduit, outlet box, bushing and connectors are available at most big box home improvement stores.

      ========

      How to Wire an Electrical Outlet Under the Kitchen Sink is a related project with under-sink outlet wiring diagrams for a non-switched outlet with flex conduit for an instant hot water dispenser. The Double Snap Lock Connector for the flex conduit to metal outlet box connection is really nice.

      Let me know if you have questions.
      Thanks,
      Bob

      • Teresa February 25, 2014 at 8:08 am #

        Hi Bob,
        Just wanted to come back and say thank you! Your information gave me the confidence to complete a project I thought I knew how to do, but needed that one piece of information to be sure. Just as a side note, I installed the disposal, completed the wiring and it didn’t work. Turned out to be a bad switch, so I had to replace it as well. The only bright side to replacing a working disposal, is that it was fifteen years old!
        Thanks again!

        • Bob Jackson February 25, 2014 at 8:23 pm #

          You’re welcome! I’m pleased my article was helpful. – Bob

  5. Paul May 25, 2014 at 11:41 am #

    Thank you very much for this detailed set of instructions. Made it very clear what materials were needed and how to go about the job. I installed the exact same disposal and not sure I would have done the whole job myself without having found these instructions. Thanks much.

  6. Susan Bramblett June 29, 2014 at 8:07 pm #

    Wow, finally, I found your instructional and it’s exactly what I have been looking for! All my questions were answered and I could stop chasing all over for answers piece-meal. I’ve not completely finished yet, so, I may have to come back again for more help. Though, with some luck and your instructions, maybe not! Thanks-a-million!

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