Which class of circuit transmits an alarm during a single open or non-simultaneous single ground fault?

• A. Class A circuit
• B. Dry-type transformer
• C. Conventional detector
• D. Class B circuit

Answer: (A)

This is about fault-tolerant signaling in fire alarm wiring. In a Class A loop, the circuit is a continuous path that can be fed from opposite ends, giving it redundancy. If a single point opens or one conductor picks up a ground fault, there’s still a complete path around the fault back to the panel, so initiating devices can still transmit an alarm. A single ground fault on one conductor (not occurring on both conductors at the same time) doesn’t break the loop, so the alarm signal reaches the panel. The other options don’t provide that loop redundancy: a dry-type transformer relates to power supply, a conventional detector is about the sensing device rather than the wiring topology, and a Class B circuit uses a single path that can be interrupted by a fault, stopping transmission.