Fire Alarm Tech


Basic Fire Alarm Terminology

NAC Notification Appliance Circuit - Term used for circuits containing Horns, Strobes, and Speakers.
IDC Initiating device circuit - Sometimes referred to as a zone, this circuit contains anything that activates the fire alarm system (ex. Pull Stations, smoke detectors, etc..). This is input only, and is an analog signal.
SLC Signaling Line Circuit - Term used for the circuit responsible for all devices on the data circuit for Addressable / Intelligent Systems. This circuit can be both input and output because the signal is digital.
AHJ Authority Having Jurisdiction - Most of the time this is the fire department that gets to make the decision on certain requirements.
Power Limited A circuit that has a fixed voltage and amperage, which cannot be changed. An example would be the DC circuits in a panel.
Non-Power Limited A circuit that is fused or has a breaker, an example would be the AC power that comes into the panel, or batteries.
Resettable Refers to devices or circuits that reset to a normal state when the system goes throught the resetting process. Resettable Power will temporarily be cut off when the system is reset.
Restorable Refers to devices that are capable of beign reused after they have been activated. Some heat detectors, for example, cannot be restored once tripped.
Trouble Used to describe anything wrong with the system, such as an open circuit or a ground fault.
Supervisory A type of signal that is used for non-fire related situations. Examples may include CO Detection and Valve Tamper Switches.
Alarm Used to describe the entire system or device in an active state. A general alarm will cause an evacuation of a building, but some other types of alarm may not.
Power Loop Sometimes known as an "active" loop, is when a circuit is outputting voltage to the highest potential. For example, this is used when a NAC goes into alarm.
Supervision Loop Sometimes known as an "inactive" loop, is when a circuit is putting out just enough voltage to ensure there is no open wire or other fault, but not enough voltage to activate a device, such as a notification appliance.