What is Fire Alarm Nominal Voltage?

To power their horns and strobes in the Notification Appliance Circuit (NAC), most fire alarm systems use Nominal Voltage. 24 volts NOMINAL is not measured as 24 volts; 24 volts NOMINAL is whatever is presently measured on the 24-volt backup battery.

The 24 volts nominal is somewhere in the range of 20 volts to 27.5 volts, depending on how well the backup battery is charged up. A fully charged 24-volt nominal backup battery will be about 27.5 volts; a nearly exhausted 24-volt nominal backup battery will be about 20 volts.

Each manufacturer uses a slightly different minimum voltage for their NAC circuit, so, when you perform voltage drop calculations, you need to look this minimum voltage for the NAC in the equipment's installation manual, or else call technical support.