Fire Prevention: How Much Voltage Can My Fire Alarm Panel Handle?

Automatic fire alarm systems can play a large role in fire prevention in your building or large home. Learning how to properly manage the power supply that each smoke detector requires can help you manage your building’s operation and maintenance. Learn How to TroubleShoot Smoke Detector Issues in Commercial Buildings.

The size of your circuit is determined by the size of the building, the number of devices, and the job’s requirements. The electricity used to power electrical devices in a building is distributed in the form of zones. A zone is a defined area in which related functional items work together. A smoke alarm circuit panel may have zones such as an alarm notification or an alarm annunciation zone. It is up to the engineer designing the system to divide the building into specific zones.

On a conventional panel, one circuit could cover one zone, but it will only tell you which circuit started alarming, not which device. In contrast, an addressable panel requires a zone-creating software to assign each smoke detector to each zone. The advantage of an addressable panel is that each device will report individually back to the panel, so you can know exactly where the alarm came from.

The more devices, the larger the panel. A single conventional zone may be able to support enough devices to cover a building, but you may be limited in the alarm annunciation zone. Remember, this zone tells you where in the building the alarm came from.

Here is an example of an addressable panel:

The number of devices you can connect to a signal circuit is based on the current rating of the circuit and the current rating of the devices connected to it. You must add up the current draw of all the devices and make sure the total does not exceed the rating of the circuit you want to connect.

For example, one smoke detector has a power output of 9 volts. If you are working with a 120-volt circuit, you would not want to exceed 10 smoke detectors.

*Please Note* It is not a good idea to exceed 80% of the circuit’s rating to give some room for expansion, and adding of square footage.

You should refer to the owner’s manual. A fire alarm will have a FWR (Full Wave Rectified) and DC current draw rating. It is important to make sure you use the correct current based on the type of power supply. For example, a panel may have a power supply rating of 3.5 amps, and include two signal circuits rated for 2 amps each. You cannot put 2 amps of signal load on both circuits, because 4 amps will exceed the panel’s total signal power.