Which component allows a control panel to supervise field wiring for open or short circuit conditions?

• A. Pip cap.
• B. Myers hub.
• C. End of line resistor.
• D. Reed switch.

Answer: (C)

In supervised alarm wiring, the panel needs a reference point to monitor the entire loop for faults. The end-of-line resistor provides that reference by placing a known resistance at the far end of the field wiring. When everything is connected and the loop is normal, the panel reads the expected resistance. If the wire opens somewhere, the circuit becomes open and the observed resistance jumps to a very high value, signaling an open fault. If a short occurs along the loop, the resistance drops away from the expected value, signaling a short fault. This allows the panel to reliably supervise the integrity of the entire field wiring. A reed switch is just a sensor, not a supervisory element; a pip cap is a splice-cap used for wiring, and a Myers hub is a junction device, neither providing line supervision.