Quick Answer
The quick answer to the question about where to connect the end of line resistor is that the only place to connect end-of-line resistor is at the end of the building's circuit.
Explanation
In any fire alarm system, the reason for the existence of the end of line resistor is to complete the electrical circuit. It allows the panel to continually check the wires to make sure the fire detection and the horns and strobes are always connected.
A fire alarm system detects fires and warns people that there's a fire. Fires happen at the wrong time; there is no right time for a fire. The fire alarm system has to be ready all the time to warn people.
Normal Electrical Path
To be ready at all times, one of the things the panel does is to supervise the wires. To supervise the wires, the panel does a continuity check of the wires by running an electrical current through all of the wires.
The pathway for the continuity-check is:
- Out of one screw terminal of the panel
- All the way to the end of the circuit through one of the wires
- Through the end of line resistor
- All of the way back to the panel through the other wire
- Into the other screw terminal of the panel
Loose Connection or Loose Wire
If something goes wrong with the fire alarm system, like a wire comes loose from a connection, the continuity path is broken and then the electricity stops.
When the electricity stops, the panel turns on its trouble light and buzzer. By turning on the light and buzzer, the panel is telling the owner to fix the system because, right now, the fire alarm system may not detect fires or warn people.
End of Line Resistor at the Panel
When the end of line resistor is in the panel instead of at the end of the circuit, the panel has a false sense of security. Even if a wire breaks or comes loose somewhere in the building, the continuity path through the end of line resistor is not broken.
In other words, the panel still thinks everything works, when in reality, some or all of the fire alarm system doesn't work.
Because the panel thinks everything is working, the panel never turns on its trouble light and buzzer. If there's a fire, the owner won't know about the broken or loose wire until the annual inspection, or until the building burns down, whichever comes first.
Alternate Answer
The installation manual that comes with the panel for the fire alarm system, and the installation sheets that come with the devices show exactly how the fire alarm system should be wired.
Sometimes there's a difference between one model of fire alarm system and another model. Always read and follow these installation manuals that come with the panels, and installation sheets that come with the devices, I do.
Douglas Krantz
