Description
The PLR Series provides a cost effective means of preventing
3-phase motor startup during adverse voltage conditions. Proper
A-B-C sequence must occur in order for the PLR’s output
contacts to energize. In addition, the relay will not energize
when an undervoltage or phase loss condition is present. The
PLR Series protects a motor against undervoltage operation.
The adjustment knob sets the undervoltage trip point.
Operation
The output relay is energized and the LED glows when all
voltages are acceptable and the phase sequence is correct.
Undervoltage must be sensed for a continuous dropout delay
period before the relay de-energizes. Reset is automatic upon
correction of the fault condition. The output relay will not
energize if a fault condition is sensed as power is applied.
Field Adjustment: Turn the adjustment knob fully
counterclockwise and apply three-phase power. The LED should
be ON. Increase adjustment until the LED goes OFF. Decrease
adjustment until LED glows again. If nuisance tripping occurs,
decrease the adjustment slightly.
NOTE: When properly adjusted and operating in an average system, a voltage unbalance of 10%
or more is required for phase loss detection. When a phase is lost while the motor is running, a
voltage will be induced into the open phase nearly equal in magnitude to the normal phase-tophase
voltage. This condition is known as regeneration. When regenerated voltages are present,
the voltage unbalance during single phasing may not exceed 10% for some motors. The PLR
Series may not provide protection under this condition. For systems that require superior phase
loss protection, select the PLMU Series.

FEATURES BENEFITS
Continuous monitoring Prevents 3-phase motor startup when undervoltage
or phase loss condition is present
Industry standard 8-pin
octal plug connection Eliminates need for special connectors
LED indication Quick visual indication of output status and correct
phase sequence