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Smoke Detector Wiring

Connecting Multiple Runs

Smoke detector wiring, ranch style house

Adding smoke detector wiring for fire protection is a good way to get the most out of a hardwired home alarm system. For monitored systems, it can also earn you a bigger discount on your homeowners’ insurance. (For more on this, see the page on Home Security Alarm Monitoring).

If you don't have a home security system, you can still add hardwired and/or wireless smoke alarms.

First Alert has many choices for replacing old hardwired smoke alarms, as well as wireless units you can install as needed.For details, see "First AlertSmoke Detectors".

Kidde also makes smoke detectors that don't require an alarm panel. They even offer a unit that lasts for 10 years and never needs a battery change! Check it out at Kidde Smoke Detectors.

Alarm Panel Fire Zones

Although many of the home security systems in use today support the connection of smoke detectors, some only provide a single fire alarm zone. This usually means connecting all of the smokes in the home on a single wire run.

This is easy to do for a simple pitched-roof style, 3-bedroom, 2-bath tract home. These homes typically have plenty of attic space across the whole house, and smoke alarm wiring can be looped from one detector to the next pretty easily.

Ranch style house can use a single fire alarm zone

With some floor plans, smoke alarm placement can make running a single smoke loop difficult if not impossible. Check out these examples:

Smoke Detector Wiring for Separated Areas

Smoke alarm placement for divided areas

The floorplan above has a vaulted ceiling separating two sections, both of which require smoke alarm wiring.

Depending on how many devices are needed on each end, you may be able to run everything on one wire. More often, there are several smokes required for both sides. It’s then simpler to make a separate pull for each side, leaving you with two wires to connect at the main panel.

Multi-Story Smoke Alarm Wiring

Smoke detector circuit for 2-story home

In this example, two different floors need smoke detector wiring. Sleeping areas upstairs and down must be covered, and pulling a smoke detector circuit for each floor is often the easiest solution.

If a basement is thrown into the mix, you may even need to pull three runs of smoke alarm wiring.

Wiring Smoke Alarms for a Detached Guest House

Wiring smoke detectors for a detached guest house

It’s a good idea to run detached buildings on their own smoke wiring. Even if they could somehow be looped in with the main house smokes, here’s a good reason not to do so:

Smoke alarm wiring (and all other wiring, for that matter) usually connects from the main house to the detached guesthouse through buried conduit. Moisture has a way of collecting in underground conduits, and can cause deterioration and corrosion of the wiring. Smoke detector problems like this can cause false alarms, aggravation, and lost sleep…

If this happens, it’s much easier to troubleshoot the problem if the two buildings have separate runs of smoke wiring. Also, if the problem is in the conduit, the guest house run can be temporarily bypassed at the alarm panel. This leaves the main house protected from fire while repairs are made to the conduit and wiring.

Connecting Multiple Runs

Each of these scenarios results in two or more smoke detector wires at the panel, with just a single fire zone to connect them to. What to do?

The solution to this dilemma is simple:

Whenever possible, pull smoke detector wiring so as to place the supervisory devices at the panel, instead of at the end-of-line smoke detector.

This is done by using “extra” pairs of wires to provide a return path from the last smoke in the run to the main alarm panel. This gives the effect of one very big loop, when in fact there are multiple runs.

For 2 wire smoke wiring, this is done by using 4-conductor wire. 2-wire smokes only require 2 conductors, but adding the extra 2 conductors allows placing the end-of-line resistor at the panel.

See how this is done here: Connecting 2 Wire Smoke Detectors.

2 Wire Smoke Detector Diagram

For 4 wire smoke detector wiring, running an extra 4-conductor wire gives the same effect. The extra run of 4-conductor wire gives us a return path to the panel. This allows you to locate the end-of-line resistor and power supervision relay at the alarm panel.

For details on how to do this, see Connecting 4 Wire Smoke Detectors.

4 Wire Smoke Detector Diagram

To complete the wiring at the panel, simply connect the feed of the first detector run to the fire alarm zone terminals, as usual.

Next, splice the return loop of the first run to the feed wires of the second run. If there is a third, or even fourth or fifth run, just follow the same pattern.

When you get to the last run, the return wires of that run will connect to the end-of-line resistor (and relay, for 4-wire smokes).

Fire alarm zone connections

And you’re done! All of the smoke detector wiring is connected to the fire alarm zone on the panel, and is fully supervised as if it were a single run! (Because, technically, it is).

For additional details on making wiring connections to smoke detector terminals, check out Smoke Detector Circuit Basics.

For guidelines on where to install smoke detectors, check out Smoke Alarm Placement for Home Security Systems.

For help finding problems with smoke alarm wiring, check out Smoke Alarm Circuit Troubleshooting for testing wiring at the main alarm panel.

For checking connections in the field, see Troubleshooting Smoke Alarm Wiring at the Detectors.

Find fire wire at

Not sure if a do-it-yourself system is right for you?

If you're just thinking about installing a do-it-yourself alarm system, you may want to know how much a professional alarm company would charge. To find out, Get Free Home Security Systems Quotes from companies in your area. This will give you a good idea of what a system would cost to have installed, as well as how much you could save by doing it yourself!

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