CAT Alarm Technician Wiring & Circuits 2 — Questions and Answers
Question 1: A supervised zone loop measures 0 ohms resistance. What condition does this indicate?
- Normal zone at rest
- Open circuit fault
- Short circuit fault (Correct answer)
- End-of-line resistor missing
Correct 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.
Question 2: Which wire type is MOST appropriate for runs near high-voltage AC power lines to prevent interference?
- Standard 18/2 unshielded
- Shielded twisted pair (Correct answer)
- Solid conductor plenum
- 18 AWG stranded unshielded
Correct answer: Shielded twisted pair
Shielded twisted pair rejects electromagnetic interference (EMI) induced by nearby AC power conductors.
Question 3: In a Class A (Style D) initiating device circuit, what distinguishes it from a Class B circuit?
- It uses a single EOL resistor
- It requires a return path so the panel can detect a wire break beyond the break point (Correct answer)
- It only supports NC contacts
- It operates at higher voltage
Correct 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.
Question 4: 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?
- Incorrect EOL resistor value
- Excessive voltage drop due to wire resistance (Correct answer)
- Panel output set too high
- Detector drawing no current
Correct 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.
Question 5: When wiring a 4-wire smoke detector, the ALARM output wires connect to:
- The auxiliary power terminals
- The initiating device circuit (IDC) zone input (Correct answer)
- The notification appliance circuit (NAC)
- The AC primary winding
Correct 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.
Question 6: Which AWG conductor size has MORE resistance per foot than 22 AWG?
- 18 AWG
- 16 AWG
- 14 AWG
- 24 AWG (Correct answer)
Correct answer: 24 AWG
Higher AWG numbers indicate thinner wire with greater resistance per unit length; 24 AWG is thinner than 22 AWG.
Question 7: A ground fault on a fire alarm circuit is MOST hazardous because it can:
- Reduce panel battery life
- Cause a simultaneous short and open, masking a real alarm (Correct answer)
- Increase EOL resistor value
- Lower NAC output voltage
Correct 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.
CAT Alarm Technician Wiring & Circuits 2
A supervised zone loop measures 0 ohms resistance.
What condition does this indicate?