How to Install a New Dishwasher

Install the Electrical Circuit 

The first step is to install a 20-amp circuit from the electrical service panel if one is not already installed. To add a circuit cable, drill a hole down through the floor into the basement or crawlspace.

Install 12 AWG cable from the dishwasher space to the service panel. Leave about six feet of cable sticking through the hole by the dishwasher. This will allow the dishwasher to be pulled out during servicing. Tape the wire to the floor with a piece of duct tape so it doesn't slip down through the hole.

Have an electrician install a new circuit breaker in the service panel and make the final wiring connections. If there is an existing circuit for the dishwasher, be sure that the power is turned off to the circuit.

Drill Holes in the Cabinets

Before you can install the drain hose and water line to the dishwasher, you'll need to drill two holes in the sink base cabinet. For the drain hose, this is a 1 1/2-inch hole located near the back of the cabinet and as high as possible without hitting the sink.

Drill the hole with a 1 1/2-inch spade bit or hole saw and a drill. The water line needs a 3/4-inch hole located in a convenient location for accessing the sink's hot water supply pipe. Drill this with a 3/4-inch bit.

Connect the Drain Hose

Insert the hose through the hole and attach it to the dishwasher drain fitting on your sink drain. If your drain doesn't have a dishwasher fitting, replace the drain tailpiece (the vertical pipe directly below the sink) with a dishwasher tailpiece (wye fitting).

An alternative is to connect to the dishwasher nipple on the garbage disposal. To use this nipple, remove the knockout in the center of the fitting hole by tapping it toward the disposer chamber (where the food goes) with a punch or screwdriver and a hammer. Remove the knockout plug (a small plastic disc) from inside the disposer chamber. Secure the drain hose to the drain fitting or disposer nipple with a hose clamp.

Connect the Water Line

To install the water line to the dishwasher, you'll need to connect to a shutoff valve on the hot water supply pipe under the sink. The easiest way to do this is to replace the existing shutoff valve with a dual-outlet shutoff valve so the same valve can serve the sink faucet and dishwasher.

Feed 3/8-inch flexible copper supply tubing through the cabinet hole and connect one end to the shutoff valve. Connect the other end to the dishwasher's water valve, following the manufacturer's directions. You'll likely need to add a brass fitting to the water valve to accommodate the 3/8-inch water line. Use thread seal tape on all connections to help prevent leaks.

Wire the Dishwasher

To access the dishwasher's wiring junction box, use a nut driver or screwdriver to remove the screws securing the base plate to the bottom front of the dishwasher. On the right side of the unit will be a metal junction box. Remove the bolt on the junction box.

Inside, you'll see a 1/2-inch hole for installing the circuit cable with a cable clamp. Feed 6 inches of cable through the clamp and tighten the clamp onto the cable. Insert the cable into the hole and install the locknut to secure the clamp. Strip the cable wires and connect the black circuit wire to the black lead in the junction box, using a wire nut. Connect the two white wires with a wire nut. Connect the bare copper circuit wire to the ground screw in the box.

Set the Dishwasher

Gently slide the dishwasher into place while carefully watching the waterline, drain hose, and electrical cable. Center the dishwasher side-to-side in the opening. Using a torpedo level as a guide, adjust the dishwasher's front feet so the unit is level and the two brackets above the door are almost touching the bottom of the countertop. Secure the unit with one wood screw driven through each bracket and into the wood base of the countertop. Be sure that the brackets are not sticking out beyond the edge of the counter. Also, make sure the screws are not so long that they can come up through the top of the countertop.

Check the Installation

The final step is to check all of the connections. First, turn on the water and make sure that there are no leaks. Next, turn on the circuit breaker feeding the dishwasher and start a dishwasher cycle. Allow the dishwasher to fill with water and start washing, then press the cancel button and let it complete the drain cycle. Be sure that there are no leaks under the sink or the dishwasher. Reinstall the base plate at the front of the dishwasher to complete the job.