Which class is prohibited for the wiring between the fire alarm control unit and the emergency function control device?

Which class is prohibited for the wiring between the fire alarm control unit and the emergency function control device?

• A. Class A
• B. Class B
• C. Class C
• D. Class D

Answer: (C)

The key idea is that signals to emergency function devices must have reliable, supervised paths so emergency actions happen even if part of the wiring is damaged. Class A circuits provide parallel, fault-tolerant paths with continuous supervision, and Class B circuits offer a single supervised path. These features are essential for interconnections between the fire alarm control unit and an emergency function control device to ensure dependable operation during a fire. Class C does not meet these reliability requirements for this kind of signaling, so wiring between the control unit and the emergency function device is prohibited to use Class C. (Class D and other classes aren’t used for these critical interconnections because they don’t meet the same signaling and supervision needs.)