Can an End of Line Relay Cause Power Failure on a Zone?

Because 4-wire smoke detectors are Normally Open devices, and loss of power doesn’t change their state, power must be supervised with a separate relay, wired in series on the smoke loop. Fire zone logic lends itself to this process by indicating trouble on open circuit, and alarm on a short.

An End of Line Relay, or End of Line Power Supervision Relay, like the EOLR-1 is a simple device that closes when it receives 12 Volts DC power. If power is lost, the relay opens, causing a trouble on the fire zone the relay is wired in series with. Wire relay power from the last smoke in line on the 4-wire smoke loop. If the smoke loses power, the relay will open and cause a trouble condition on the 4-wire smoke zone. As long as the EOLR-1 is wired correctly, as shown above, it can not cause a power failure on a zone.

NOTE: In order to cut down on confusion with this wiring diagram, references to power reset for the smokes has been removed. 4-wire smokes latch on alarm, and will require that power to the zone be dropped momentarily in order to reset them afterward. For more that, click here.