This project is continued from Part 1.
Kidde/Firex® Smoke Alarm
The smoke alarms in my house are 10 years old and will be replaced with new Kidde/Firex® Dual Sensor (Ionization and Photoelectric) 120VAC powered hardwired alarms with battery backup. I chose the Consumer Reports #1 rated Kidde PI2010 alarm that sells for about $30.
The alarm includes the 9 volt battery – a nice touch to get started.
Smoke Alarm Wiring Diagram
In Part 1, I described how the smoke alarm in the finished basement was disabled and improperly located in a crawl space. The scope of work for this project is to:
- Remove the old smoke detector and ceiling electrical box.
- Wire and install a new smoke detectors in both the finished and unfinished sections of the basement.
120VAC power for the smoke alarms will provided by a new branch circuit from an existing junction box on a continuous (i.e. non-switched) circuit. The new work is indicated by the green box in this wiring diagram:
The smoke detectors are hardwired as follows:
- 120VAC power is provided by the hot (black) and neutral (white) wires.
- Interconnect alarm signaling is carried by the red wire. If one alarm goes off, it will signal the other alarms to sound.
- The neutral (bare copper) wire is not used by the smoke alarms and no connection is required. However, I connect the ground wires between the different cable runs as a matter of personal preference. A continuous ground wire is your friend in safety.
If you’re not comfortable and experienced working with 120VAC wiring, I strongly recommend that you hire a licensed electrician to do the work.
Smoke Alarm Placement
- On every level of the home, including the basement.
- On the ceiling if possible, at least 4 inches away from the wall.
- Outside of every bedroom on older homes to comply with the old rules.
- New homes must have a smoke alarm in every bedroom and all smoke alarms must be interconnected.
Do not install smoke alarms:
- Near windows, doors and heating/cooling vents because drafts can interfere with the detector.
- In the attic.
- In crawlspaces.
Smoke Alarm Installation Tools
The following tools were needed to wire and install the smoke alarms, moving clockwise from the top these are:
- Drywall jab saw
- Cordless drill/driver
- Needle nose pliers with cutter
- Wire stripper / cutter
- Utility knife
- Non-contact voltage detector
NM-B 14/3 and NM-B 14/2 Cable
Before I begin wiring the new smoke alarm, I’ll take a moment to explain the two types of electrical wire that I’ll be using.
NM-B 14/3 wire means Non-Metallic 14 gauge, 3 conductor plus ground. The ‘B‘ designates the application – for exposed or concealed work in normally dry locations. The conductors are:
- Hot (black) or line side.
- Neutral (white).
- Red – used here for alarm interconnect signaling, so if one alarm goes off, they all sound.
plus the bare copper ground wire. The smoke detectors are ungrounded and the ground wire is not used.
NM-B 14/2 is a 14 gauge, 2 conductor plus ground wire. Two conductors are:
- Hot (black) or line side.
- Neutral (white).
I used NM 14/2 wire to run a new AC branch feeder circuit to power the alarms (see the junction box at the far right of the above wiring diagram).
For brevity, I use “NM” when referring to “NM-B” in this project. I also use the terms “wire” and “cable” somewhat interchangeably. Cable generally refers to the entire NM-B wire bundle, and wire refers to an individual conductor.
Unfinished Basement Smoke Alarm Installation
I began by removing the old smoke alarm and ceiling box from the crawlspace in the finished basement; recall that I determined after careful analysis there is no AC power on the alarm circuits. The new smoke alarm will be located nearby in the unfinished area of the basement where the gas furnace, gas water heater and my workshop are located. The new position is only about 5 feet away but in a much more accessible location. I’ll reuse the existing NM 14/3 wire that interconnects to the the other smoke alarms in the house.
Smoke Alarm Ceiling Junction Box Wiring
An octagonal ceiling box is installed on the floor joist to wire in the new smoke alarm. The existing NM 14/3 alarm wire from the upper floors is brought in on the left and new cables are brought in on the right side: NM 14/2 for power and NM 14/3 for the second smoke alarm to be installed in the finished basement area.
Note: The smoke alarm trim plate will not fit a 4″ square junction box, you must use an octagonal or rectangular ceiling box. I chose the octagonal box because it can handle four cables without over crowding.
The above photo corresponds to these cables in the wiring diagram:
The wires are matched by color, twisted together and secured by a wire nut to the Kidde PI2010 AC Quick Connect Harness. A #10-32 green ground screw and ground wire pigtail is fastened to the junction box, then twisted and nutted with the other ground wires. Metal junction boxes must be grounded per the National Electrical Code (NEC).
The wires are tucked into the ceiling box with the AC Quick Connect hanging down as shown:
The AC Quick Connect pigtail is inserted through the trim plate, the trim plate fastened to the octagonal ceiling box with two screws (included with the ceiling box) and the AC Quick Connect plugged into the smoke alarm.
The smoke alarm is mounted to the trim plate by twisting on until it ratchets into place.
120VAC Branch Circuit Wiring for Smoke Alarm
A new run of NM 14/2 cable is installed between the octagonal ceiling box and a convenient junction box on the wall about 10 feet away. The junction box is on a circuit that is connected at the main electrical panel. It’s extremely important the smoke alarms are on a continuous non-switched circuit and not behind a light switch.
The new circuit for the AC power feed installed in the next step is highlighted in this portion of the wiring diagram:
Be certain to shut off the circuit breaker and confirm the circuit is dead with your voltage detector before continuing!
The new NM 14/2 cable run for the smoke alarm power feed is brought into the existing junction box and wired in as shown below. Remember to secure your new cable with wire staples within 1 foot of the junction box and every 4 or 5 feet along the floor joists or 2×4 wall studs.
If you don’t have a junction box to wire into, you can splice into an existing circuit as explained in this project.
Jumping ahead to when I’ve installed the 2nd smoke detector and completed all the wiring, the green AC power indicator glows when the alarm is on 120VAC power. For now, the circuit breaker and AC power must remain off.
Now I’m ready to install a second smoke detector in the finished section of the basement in Part 3.
Thanks for reading,
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