Where should a fire EOLR be installed?

• A. at the last device and never inside the control or across the zone defined as fire
• B. Inside the control panel
• C. At the first device
• D. In the non-fire zone

Answer: (A)

End-of-line resistance is used to supervise a fire alarm signaling loop. It must be placed at the far end of the circuit—the last device on the fire loop—so the control panel can detect any interruption or short anywhere along the path from the panel to that last device. If the resistor were inside the control panel, end-of-line supervision would be lost on the field wiring. If it were placed at the first device, faults beyond that point wouldn’t be detected. Placing it in a non-fire zone or across zones would violate zoning and could mask faults. So the correct placement is at the last device in the fire zone.