Alarm Signal. A signal that indicates the presence of an emergency requiring immediate action, such as
an alarm for fire from a manual station, a waterflow alarm, or a automatic smoke detector.
Alarm System. A combination of compatible initiating devices, control units, and notification appliances
designed and installed to produce an alarm signal in the event of a fire.
Audible Signal. A sound made by one or more audible notification appliances, such as bells or horns, in
response to the operation of an initiating device.
Authority Having Jurisdiction (AHJ). The organization, office, or individual responsible for approving
equipment, installations or procedures.
Class A Circuit. An initiating device or notification appliance circuit in which all components remain fully
functional when a single open or ground exists in the circuit.
Class B Circuit. An initiating device or notification appliance circuit in which some or all components may
be disabled when a single open or ground exists in the circuit.
End Of Line (EOL). A device used to terminate a supervised circuit.
General Alarm. A term usually applied to the simultaneous operation of all the notification appliances on
Ground Fault. A trouble condition in which a low resistance has been detected between the system
wiring and conduit ground.
Initiating Device Circuit (IDC). A circuit to which initiating devices are connected.
Labeled. Equipment or materials to which a label, symbol, or other identifying mark of an organization
acceptable to the AHJ and concerned with product evaluation has been attached. The organization's
label indicates that the manufacturer complies with appropriate standards, performs in a specified manner
and maintains periodic inspection of the production of such labeled equipment or materials.
Listed. Equipment or materials included in a list published by an organization acceptable to the AHJ and
concerned with product evaluation. Inclusion in the list indicates that the equipment or materials comply
with appropriate standards, and has been found suitable for use in a specified manner. The manufacturer
maintains periodic inspection of production of listed equipment or materials.
NEC. National Electrical Code also published as NFPA standard 70.
Notification Appliance. An electrically operated appliance used to indicate the system status such as a
bell, horn, strobe light or speaker.
Notification Appliance Circuit (NAC). A circuit to which notification appliances are connected.
Power Supply. That portion of the fire alarm control unit which provides the power needed to operate all
control unit modules, as well as that, needed to operate all electrically powered initiating devices and all
Trouble Signal. An audible signal indicating trouble of any nature, such as a circuit break or ground,
occurring in the device or wiring associated with a fire alarm signal.
Zone. A designated area of a building. Zone is commonly interchanged with initiating device circuit.