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Diagram of Class A Wiring

Free PDF Diagram:

Fire Alarm System Class A Wiring

See how to wire a fire alarm system using Class A Wiring.

See how the Class A Wiring changes to 2 Class B Circuits when a wire breaks.




Class A Wiring is an automatic safety backup for the building fire alarm system wiring. Under normal circumstances, all devices are connected to the fire alarm panel. With Class A Wiring, when a single wire breaks, all of the devices are still connected to the fire alarm panel.

The Diagram Shows:
  • How the wires connect from the fire alarm panel, to each device on the Class A Wiring loop, and back to the fire alarm panel.
  • The supervision current path along the wires, from the Class B Wiring output of the panel, through each wire in the building system, and back to the Class A Wiring input of the panel.
  • What the system does to automatically change from a single Class A Wiring scheme to 2 Class B Wiring Loops when a single wire breaks somewhere in the building.