How to Power a Smoke Detector Without a Battery

If you’re not going to use battery to power your smoke detector, it’s going to be hard wired. The advantage is that you can interconnect smoke detectors so that when one goes off the others sound their alarms too. This protects your family better, especially if your bedrooms are spread apart from each other.

Step 1: Calculate the Load and Circuit Capacity

New Construction

New construction smoke detectors should be installed on a dedicated circuit. To calculate how many smoke detectors can be installed on one dedicated circuit use the following equation.

First, calculate the circuit capacity, in watts, by multiplying the circuit voltage times the amperage of the circuit breaker. Next, reduce the product to 80 percent and that equals the maximum capacity of this circuit in watts.

Now, determine the power consumption, in watts, of each smoke detector from the manufacturer’s documentation or look on the back of the smoke detector. Lastly, divide the circuit capacity by the smoke detector power consumption and the product equals the number of smoke detectors you can connect to your dedicated circuit.

Remodel

To add a smoke detector to existing circuitry you must first determine if the existing circuit can handle the load of the smoke detector. To do this, use the following equation.

First, figure out which branch circuit breaker controls the existing circuit you are considering. Turn the circuit breaker off and on to identify all the electrical lighting and appliance loads connected to that circuit. Then, total the wattages of all the loads connected to that circuit to determine your total connected load.

Next, calculate the circuit capacity, in watts, by multiplying the circuit voltage times the amperage of the circuit breaker, typically listed on the breaker handle. Reduce the product to eighty percent and that is the maximum capacity of this circuit in watts.

Lastly, subtract your total connected watts from the reduced circuit capacity and the difference is the maximum wattage available for adding smoke detectors. Adding a smoke detector must not exceed the circuit capacity. Divide the available circuit capacity by the power consumption, in watts, of each smoke detector to determine how many smoke detectors your existing circuit can handle. Make sure the smoke detectors you buy match the voltage of the existing circuit.

Step 2: Size the Wire

Size the wire according to the existing circuit rating or the rating of the dedicated circuit. Typically, 14 or 12 gauge romex is used in homes. Use two conductor romex to power the first smoke detector, then use three conductor romex from smoke detector to smoke detector. The third conductor serves as an interconnect wire between the smoke detectors so that smoke detectors can communicate with each other.

 Step 3: Site Considerations

Placement of your smoke detector is critical. Generally, smoke detectors are placed in bedrooms or in the hallways of adjacent bedrooms, at least 12 inches away from any corner. Usually, one smoke detector is placed on each level of a structure. Follow the manufacture’s instructions for placement and check for local codes and requirements.