How to Install Hardwired Smoke Detectors

Smoke Detector Placement and Features
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Smoke detectors protect your family from smoke and fires in your home because these two things can catch you off guard while you’re in a deep sleep. Fires and smoke inhalation injure and kill many people each year. By having smoke detectors in and around bedrooms and hallways, these tragedies can be avoided.

Hardwired smoke detectors are wired so that if one detector warns of smoke or fire, the others also go off. This way, all areas of the home are warned. The other nice feature is battery backup. The detector runs on 125-volt power until the power goes out. Then the battery kicks in and keeps right on protecting you!

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Cut in Boxes
Determine the appropriate location for the smoke detectors in your home and cut in boxes in the upper walls or ceilings. When installing in the walls, usually the detectors are mounted around 12″ below the ceiling. Use a stud finder to locate the wall studs, so the box doesn’t end up on a stud.

Hold the cut-in box up on the wall and use a level to mark the outside of the box. Mark this in pencil, not marker. If you are installing the boxes in the ceiling, locate the ceiling joists and cut next to them. This will give you nice box support. After all are marked, use a drywall saw to cut the holes in the drywall.

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Install Electrical Wires
Install electrical wires from the electrical panel or fuse box to the smoke detectors. First, run a 12-2 NMB with the ground wire from the panel to the first box. This will give you a hot, neutral and ground wire. Mark “hot wire” on this piece of wire at the box.

Next, run a 12-3 NMB wire with the ground from the first box to the second box. If there are more than two boxes, run a 12-3 NMB with the ground wire to each of these boxes also. No box should have more than two wires in it when you are finished.

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Making the Connections
In the first box, connect the two black wires together and add the black wire from the smoke detector connection. Now tie all the white wires together. Tie the bare copper ground wires together and run a pigtail to bond it to the box. Connect the red wire to the interconnect wire from the smoke detector. This wire will usually be marked and is usually a yellow wire. Make each connection with a wire nut big enough to cover all exposed wires.

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Install the Mounting Bracket
Place the smoke detector mounting bracket over the box opening and align with the two screw holes. Make sure that the wire connection is fed through the center hole of the bracket. Install the appropriately sized screws and tighten the mounting bracket in place.

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Plug in the Smoke Detector Feed
At the back of the smoke detector, you will find a three-pronged connection. This is where the plug that you just wired will attach to the smoke detector. It is configured so that you can only plug it in one way.

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Insert the Smoke Detector Battery
Open the battery cover in the back of the smoke detector. Notice that the positive and negative are marked both on the detector and the battery. Install the battery positive to positive, negative to negative, and replace the cover.

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Connect the Smoke Detector to the Base
Grab the smoke detector in your hands and align the slots in the back of the smoke detector with the notches on the base. Twist the detector until it locks into place. Check to see that both sides are snug and secure.

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Connect the Feed Side Wire
Strip the end of the non-metallic sheathed (NMB) wire and connect the ground wire (bare copper wire) to the ground buss. Connect the white wire to the neutral bus.

CAUTION! Before connecting the black wire to the breaker, make sure the breaker is in the OFF position. Now, connect the black wire to a 20-amp breaker or fuse. Mark the panel schedule with the placement location of the breaker you connected to.

If there isn’t a spare breaker, you can either add a breaker or connect it to an existing circuit that doesn’t have much connection to it.

Continue to 10 of 10 below.

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Turn on the Circuit and Test the Smoke Detector
Replace the panel cover and turn the circuit on that controls the smoke detectors.

CAUTION! Look away when turning on the breaker and step to one side of the panel. Never stand directly in front of a panel when turning on and off breakers.

Go to the smoke detector and push the test button. You’ll need to hold the button in for a few seconds until it sounds an alarm. Be sure to have someone walk around to all of the other detectors to check if they are also going off. With the interconnection wire, they should all be sounding.

Release the button, and it should go silent again. That’s all there is to installing smoke detectors. Remember to always replace the batteries once a year with long life type batteries. A few minutes installing and checking these devices can save your life!

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