Adding a Dishwasher: Two-Branch Valve, Tailpiece and Plug Wiring

Wiring a dishwasher plug looks like three wires to three wires, yet the plug has two gray wires with copper and one green, so there is a 50 percent chance of getting it wrong. This Old House plumbing and heating expert Richard Trethewey shows how to tell them apart while adding a new dishwasher to a kitchen.

Hot water supply

The job starts at the pipe feeding hot water to the kitchen sink. Trethewey replaces its shutoff with a similar valve that has two branches, one for the kitchen sink and one for the dishwasher. The water is already shut off in the basement before he breaks the connections.

On a compression connection, the nut goes onto the pipe first, then a brass ferrule, and tightening the nut compresses the ferrule so hard that it fuses into the pipe. The existing pipe already has a fully compressed ferrule and nut, so he reuses them on the new valve. The old sink supply hose goes on one branch. He says shutoff valves belong under every fixture, because the faucet or the dishwasher will someday need repair.

The dishwasher gets a stainless steel braided hose. That hose has its nut already on it, so no ferrule is needed; it is still called a compression connection and makes a watertight seal.

Discharge hose

With a garbage disposal, the hose fits a branch on the side. Here there is none, so the existing tailpiece is replaced with a dishwasher tailpiece made for this connection. A special top gasket goes on and the nut comes up, and a reused nut with a built-in gasket fits at the bottom.

Water and power on the unit

The dishwasher is tipped back to reach the connections at the front bottom. An adapter elbow, already wrapped in Teflon tape, is threaded in carefully so the threads are not mangled. The braided line has to fit into the trough between the unit and the floor.

For the electrical connection, the unit has black (hot), white (neutral) and green (ground). On the appliance plug, one side is smooth and the other ribbed. The smooth side is the hot and goes to black. It is a polarized plug, so it matters. The ground is connected last.

Setting the dishwasher

The water line is taped in place so it fits the narrow groove beneath the unit, and the dishwasher is lifted in without scratching the floor. It is clamped to the underside of the countertop and leveled. The drain hose is secured as high as possible inside the cabinet so that if the sink ever backed up, the dirty water would not flow into the dishwasher.

With the water back on there are no leaks. The power is plugged in, and pressing the power button brings up a jingle.