Alarm Technician Wiring & Circuits Flashcards

A supervised zone loop measures 0 ohms resistance. What condition does this indicate?

Answer: Short circuit fault

Zero ohms across a supervised zone indicates a short circuit, which bypasses the end-of-line resistor and causes a fault condition.

Which wire type is MOST appropriate for runs near high-voltage AC power lines to prevent interference?

Answer: Shielded twisted pair

Shielded twisted pair rejects electromagnetic interference (EMI) induced by nearby AC power conductors.

In a Class A (Style D) initiating device circuit, what distinguishes it from a Class B circuit?

Answer: It requires a return path so the panel can detect a wire break beyond the break point

Class A wiring returns from the last device back to the panel, allowing the panel to continue supervising devices beyond an open-circuit fault.

A technician measures 13.8 VDC at the panel but only 11.2 VDC at the last detector on a long run. What is the most likely cause?

Answer: Excessive voltage drop due to wire resistance

Voltage drop across the wire resistance (V = I × R) reduces available voltage at the end of a long loop.

When wiring a 4-wire smoke detector, the ALARM output wires connect to:

Answer: The initiating device circuit (IDC) zone input

The two power wires supply the detector; the two alarm wires connect to the panel's IDC zone to report an alarm.

Which AWG conductor size has MORE resistance per foot than 22 AWG?

Answer: 24 AWG

Higher AWG numbers indicate thinner wire with greater resistance per unit length; 24 AWG is thinner than 22 AWG.

A ground fault on a fire alarm circuit is MOST hazardous because it can:

Answer: Cause a simultaneous short and open, masking a real alarm

A ground fault can create false indications or prevent the system from detecting an actual alarm condition, making it a safety-critical fault.