Although building codes sometimes allow builders to hard-wire garbage disposals to dedicated switches, most builders choose to wire the disposal to a power cord, which they plug into a switch-operated, under-cabinet receptacle. Plug-wired disposals are not only easier to install, but also quick to remove during under-sink plumbing repairs. Most disposal manufacturers provide a power cord with new units. If your disposal doesn’t include a cord, you can find one at a standard home improvement store, usually labeled as an “appliance cord” or “garbage disposal cord.” With just novice electrical skills and common hand tools, you can wire your disposal for standard installation.
Breakers and Circuits - Although electrical requirements vary according to building codes and manufacturers' specifications, most garbage disposal units have a dedicated circuit, usually from a 20 amp breaker. The term dedicated circuit means that the only appliance served by the breaker is the garbage disposal. Garbage disposals use brief, powerful bursts of electricity, which often short-out circuits when used at the same time as other appliances. The garbage disposal's circuit usually powers to an switch-operated electrical receptacle beneath the kitchen sink. Most building codes require builders to install the garbage disposal's switch within several feet of the appliance. If wired correctly, one of the receptacles outlets is "always hot," meaning always on, and can power an adjacent dishwasher.
Switch-to-Receptacle Wiring - Wiring specifics vary according to your project's circumstances. In many cases, the disposal's dedicated circuit runs from the breaker to the under-sink receptacle. The wiring attaches to one of the receptacle's outlets to provide power for an "always hot" plug, which might power an adjacent dishwasher. The hot wire leaves the receptacle's box and runs to the above-counter switch that will control the receptacle's remaining outlet, which will serve the disposal's power cord. After connecting to the switch, the wire returns the receptacle and connects to the remaining outlet.
Wiring the Disposal's Cord - The disposal's wires are usually tucked within the appliance and contained with a protective metal plate. Connecting the disposal's wires to an appliance cord is relatively straightforward. Both sides of the connection typically have a hot, neutral and ground wire. The ground wires connect to the disposal's grounding screw and the hot and neutral wires join. The protective plate cover and a specially designed wire clamp secure the cord to the bottom of the disposal. Before plugging in the disposal, you should turn the receptacle's switch to the off position.
Working Safely with Electricity - To prevent serious injury or death, you must shut off the breaker that supplies power to the circuit you are working. If in doubt about which breaker to turn off, you should turn off the main breaker. Additionally, most municipalities require permits and inspections for rewiring projects. You must consult your local building authority before adding circuits to your home and running wires to your kitchen. If you're unfamiliar with wiring, you should consult a professional before attempting electrical projects.