How to Hardwire a Smoke Detector

It is important that the feed for the smoke detector comes directly from the electrical panel. You do not want to pick up an existing feed inside the home. For guides on how to install a new circuit and how to run wire across a ceiling or between floors, check out the links available in Resources below. For this tutorial, we will cover the wiring aspect of the smoke detector. (Of course, the circuit should not be connected in the panel yet, that is the last part of the job.)

When you are planning to hardwire a smoke detector, positioning is everything. It is recommended by the National Electric Code to install smoke detectors on every level of your home, directly outside of the bedroom doors.

At this point, we will pick up the job with the old-work box installed in the ceiling or wall, and about 6 inches of 12-2 or 14-2 NM cable hanging out of it. Use the electrical wire strippers to make a cut in the outside sheath of the NM cable. Cut away the exterior sheath and any paper insulator. This should leave you with just the three independent wires.

Use your wire strippers to strip about 3/4 inches of insulation from the ends of each of the wires coming out of the box.

The wiring harness that comes with the smoke detector comes in two parts: the part that is fixed to the detector itself and the part that has wires coming out of it. Take the part that has the wires coming out of it.

There should be three wires coming out of the harness: a black, a white and a yellow. The yellow wire is for wiring more than one smoke detector in parallel. We will go over that in another guide. Since this is for a single-floor residence, we only need the one smoke detector, so place a wire connector over the yellow wire; you will not be needing it here. Next, secure the bare or green wire to the wall box using a ground screw. Then, connect the white harness wire to the white wire coming out of the box. The black harness wire gets connected to the black wire coming out of the box. Secure each pair with wire connectors and wrap a strip of electrical tape around the base of each connector.

Fish the harness through the smoke detector's mounting bracket and secure the bracket to the wall box. Then, plug the wiring harness into the jack on the backside of the smoke detector and mount the detector on the bracket.

Now, just make the connections in the electrical panel by following the instructions in the guide available below. With the circuit now on, you should see the "ready" light illuminated on the detector. Press the "test" button on the smoke detector to make sure it is working. With the test complete and successful, insert the backup battery and you're all finished!