Which circuit is designated as a fail-safe circuit in fire alarm terminology?

Which circuit is designated as a fail-safe circuit in fire alarm terminology?

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

Answer: (D)

Fail-safe means the circuit is wired so that a fault will trigger an alarm or warning, not go unnoticed. In fire alarm terminology, Class D is designated as the fail-safe type because its design ensures that if any part of the circuit fails or a fault occurs, the system moves into an alarm or supervisory state to alert occupants. This prioritizes safety by preventing hidden faults. The other circuit types focus on different fault-tolerance characteristics rather than guaranteeing an alarm on fault; they describe how signaling paths are arranged (for example, looping or single-path configurations) but do not carry the explicit fail-safe designation.

Fail-safe means the circuit is wired so that a fault will trigger an alarm or warning, not go unnoticed. In fire alarm terminology, Class D is designated as the fail-safe type because its design ensures that if any part of the circuit fails or a fault occurs, the system moves into an alarm or supervisory state to alert occupants. This prioritizes safety by preventing hidden faults.

The other circuit types focus on different fault-tolerance characteristics rather than guaranteeing an alarm on fault; they describe how signaling paths are arranged (for example, looping or single-path configurations) but do not carry the explicit fail-safe designation.