Series: PLR

The PLR series is a cost-effective, three-phase voltage monitor that prevents three-phase motor startups during adverse voltage conditions. The proper A-B-C sequence must occur in order for the monitor’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-to-phase 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.