© 2016 Littelfuse Protection Relays & Controls

www.littelfuse.com/

Rev: 1-A-062716

Protection Relays

Voltage Monitoring Relays

www.littelfuse.com/plr

PLR SERIES

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-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.

Features & Benefits

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

Ordering Information

MODEL

LINE VOLTAGE

PLR120A

95 to 140VAC

PLR240A

190 to 270VAC

PLR380A

340 to 450VAC

PLR480A

380 to 500VAC

If you don’t find the part you need, call us for a custom product 800-843-8848

Wiring Diagram

F = Fuses

ØA = Phase A = L1

ØB = Phase B = L2

ØC = Phase C = L3

NO = Normally Open

NC = Normally Closed

Relay contacts are isolated

2A fast acting fuses recommended for

safety (not required).

8-PIN