How to Connect Smoke Detectors in Parallel (10 Steps)

By the end of this article, you will be able to connect a smoke detector in parallel.

In modern homes, smoke detectors are a must. Typically, you install fire alarms in every room in your home. But without a proper connection process, all efforts can be in vain. What do I mean by correct wiring? Smoke detectors must be connected in parallel. That way, when one fire alarm goes off, all the alarms in your house go off. In this guide, I'll show you how to do it in a few easy steps.

As a general rule, for parallel installation of wired smoke detectors, follow this procedure.

• Purchase the required 12-2 NM and 12-3 NM cable.
• Cut the drywall according to the number of smoke detectors.
• Turn off the power.
• Pull the 12-2 Nm cable from the main panel to the first smoke detector.
• Fish out the 12-3 NM cable from the second fire detector to the third. Do the same for the rest of the smoke detectors.
• Install old work boxes.
• Strip three wires.
• Connect the wiring harnesses to the smoke detectors.
• Install a smoke alarm.
• Check smoke detectors and insert backup battery.

The above 10 step guide will help you set up multiple smoke detectors in parallel.

Follow the article below for a complete guide.

10 Step Guide to Paralleling Smoke Detectors

Things You'll Need

• Three fire detectors
• Three old work boxes
• Cable 12-3 Nm
• Cable 12-2 Nm
• For stripping wires
• Drywall Saw
• Screwdrivers
• Few wire connectors
• Insulating tape
• Measuring tape
• Non-metal fish tape
• Notepad and pencil
• Нож

Remember about: In this guide, I use only three smoke detectors. But depending on your requirements, use any number of fire detectors for your home.

Step 1 - Measure and Buy

Start the process by measuring the length of the cables.

Basically you will need two different cables during this connection process; Cables 12-2 Nm and 12-3 Nm.

From electrical panel to 1st smoke detector

First measure the length from the panel to the 1st alarm clock. Record the measurement. This is the length of the 12-2nm cables you will need for this process.

From the 1st smoke detector to the 2nd and 3rd

Then measure the length from 1^st alarm clock for the second. Then measure from 2^nd in 3^rd. Write down these two lengths. Buy 12-3nm cables according to these two measurements.

Step 2 - Cut the Drywall

Take a drywall saw and start cutting the drywall into 1^st smoke alarm location.

Start cutting according to the size of the old working box. Do the same for the rest of the locations (2^nd and 3^rd signaling locations).

Step 3 - Turn off the power

Open the main panel and turn off the power. Or, turn off the circuit breaker that supplies power to the smoke detectors.

Remember about: When powering three or four smoke detectors, you will need a dedicated circuit breaker. So, install a new switch with the appropriate amperage. Hire an electrician for this task if necessary.

Step 4 - Catch the 12-2 NM Cable

Then take a 12-2 Nm cable and run it from the main panel to 1^st smoke alarm.

Use fish tape to complete this step. Don't forget to connect the wires to the circuit breaker.

Step 5 - Catch the 12-3 NM Cable

Now catch the 12-3 NM cable from the 1st to the 2nd alarm. Do the same for 2^nd and 3^rd smoke detectors. If you have access to the attic, this step will be much easier. (1)

Step 6 - Install Old Work Boxes

After catching wires, you can install old work boxes. However, the wires must extend at least 10 inches from the old working box. So, draw out the wires appropriately and install the old working boxes by tightening the wing screws.

Step 7 - Strip the Wires

Then we move on to 3^rd smoke alarm location. Remove the outer insulation of the NM cable. You will get red, white, black and bare wire with NM cable. The bare wire is ground. Connect it to the work box with the ground screw.

Then strip each wire with a wire stripper. Loosen ¾ inch of each wire. Apply the same technique to the other two smoke detectors.

Step 8 - Connect the wiring harness

With every fire alarm you will receive a wiring harness.

There should be three wires in the harness: black, white and red. Some harnesses come with yellow wire instead of red.

1. Take 3^rd smoke alarm wiring harness.
2. Connect the red wire of the harness to the red wire of the NM cable.
3. Do the same for the white and black wires.
4. Use wire nuts to secure the connections.

Then go to 2^nd smoke alarm. Connect the two red wires coming from the work box to the red wire of the wiring harness.

Do the same for the black and white wires.

Use wire nuts accordingly. Repeat process for 1^st smoke alarm.

Step 9 - Install a Smoke Alarm

After completing the wiring process, you can install the mounting bracket on the old working box.

Make holes on the mounting bracket if necessary.

Then insert the wiring harness into the smoke detector.

Then attach the smoke detector to the mounting bracket.

Remember about: Follow this process for all three smoke detectors.

Step 10. Check the alarm and insert a backup battery.

All three fire detectors are now properly installed.

Turn on the power. Find the test button on 1^st alarm and press it for a test run.

You should hear all three beeps at the same time. Press the test button again to turn off the fire alarm.

Finally, pull out the plastic tab to activate the backup battery.

Summing up

Connecting multiple fire detectors in parallel is a great security feature for your home. If there is a sudden fire in the basement, you will be able to detect it from your living room or bedroom. So, if you haven't wired smoke detectors in parallel yet, do so today. (2)

Take a look at some of our articles below.

• Which wire to connect two 12V batteries in parallel?
• How to connect ground wires to each other
• How to connect several lamps to one cord

Recommendations

(1) loft - https://www.britannica.com/technology/attic

(2) living room or bedroom - https://www.houzz.com/magazine/it-can-work-when-your-living-room-is-your-bedroom-stsetivw-vs~92770858

Video links

How to Replace Hardwired Smoke Detector – Safely Update Your Smoke Detectors with Kidde FireX

How to Install Smoke and Carbon Monoxide Detectors | Ask This Old House

How To Install Ceiling Light Without Existing Wiring