How to Wire a Switch Under the Sink

Put the switch for the garbage disposal under the kitchen sink

The most common use for an under-sink switch is for a garbage disposal, but it can conceivably be used for anything. You will need a surface-mount switch box and a convenient place to locate it. While you should use a GFCI (Ground Fault Current Interrupting) switch, you may have trouble finding one. If you can't, use a normal switch but remember that if the switch is being used to power an under-sink receptacle, it will have to be a GFCI receptacle. All wires that you run under the sink should be in electrical conduit.

Things You'll Need

• Surface-mount electrical box
• Wire clamp
• Conduit adaptor
• Electrical conduit
• Screwdriver
• Channel locking pliers
• 1.5 inch screws
• Switch
• Utility knife
• Wire splicer
• Pliers
• Twist-on wire connector
• Switch cover plate

Instructions

1. Knock out two convenient holes from a surface-mount electrical box with a screwdriver and insert conduit adaptors in each hole with the wire clamp on the inside of the box. Tighten the nut on the threaded end of the adaptors with channel locking pliers.

2. Determine the location of the switch and screw the box to a nearby stud, shelf support or other stable piece of wood with two 1.5-inch screws.

3. Attach the conduit carrying the house wire to one of the adaptors and pull the house electrical wire through the clamp so that you have about 8 inches to work with. Tighten the clamp with a screwdriver. Pull the same amount of the load wire through the second conduit adaptor and tighten the clamp. The conduit for the load wire can be added later if it is not already covering the wire.

4. Use a utility knife to remove about six inches of sheathing from both of the wires. Cut around the circumference of the sheathing, being careful not to cut into the insulation on the wires themselves, and pull it off with pliers.

5. Remove about 1/2-inch of insulation from the ends of all of the black and white wires. Hold the ends of the white wires from the house and to the load together so that they are parallel and twist them together clockwise with pliers. When they are firmly joined, screw on a wire connector.

6. Insert the ends of the black wires into the holes behind the brass screws on the switch. If there are no holes, hook the wires clockwise around the screws and tighten them with a screwdriver.

7. Twist the ground wires together. You do not need to cap these, but if the electrical box is metal, you need to attach them to the grounding screw on the box.

8. Attach the switch to the electrical box using the screws that came with the switch. Make sure the switch is straight before you tighten the screws. Then affix on the cover plate with the provided screws.

Tips & Warnings

• Make sure the power is off before you do any cutting or splicing of electrical wires. If you are not sure, test the house wire with a voltage tester.

References

• Fine Home Building: wiring a single-pole switch
• Reader's Digest: surface-mounted wiring