WiremanWireman · Fire alarm panel trouble: open circuit: troubleshooting for electricians · 2023 NEC ·
Fire alarm panel trouble: open circuit
Supervised circuits, end-of-line resistors, loose terminals and removed devices.
Before you start
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How it works
Conventional fire alarm circuits are supervised: the panel sends a small current through the wiring to an end-of-line resistor (EOLR) at the last device and back. If the wire breaks, a terminal loosens or a device is removed, the current stops and the panel reports an open circuit trouble. Class A circuits loop back to the panel instead of ending at a resistor. In many places only licensed fire alarm personnel can do this work, and the monitoring company and AHJ must be notified first.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- Are you licensed or authorized for this system, and has the monitoring company been notified?
- Yes, notified and in testWas anything recently removed, replaced or painted?
- A detector or device was removedDevice removed from its base
- No known changesTest: Measure the circuit at the panelExpect: About the EOLR value plus a few ohms of wire resistance.
- Open (OL)Test: Find the break
- EOLR missing or brokenMissing or failed end-of-line resistor
- Loose terminal or broken wire at a deviceLoose terminal or broken conductor
- Break in the cable between devicesBroken cable between devices
- Close to the EOLR valuePanel input or termination
- Wrong value or near 0 ΩWrong resistor or a short
- Open (OL)Test: Find the break
- NoNotify first, or bring in the licensed fire alarm technician
- Yes, notified and in testWas anything recently removed, replaced or painted?