© 2016 Littelfuse Protection Relays & Controls
Protection Relays
Voltage Monitoring Relays
www.littelfuse.com/plm
Rev: 1-A-062116
PLM SERIES
Voltage Monitor
Description
The PLM Series is a 3-phase voltage monitor that continuously
monitors each of the three phases. Monitors both delta and
wye systems and no connection to neutral is required. The
microcontroller circuit design protects against undervoltage,
voltage unbalance, phase loss and phase reversal. Protection is
assured when regenerated voltages are present.
Operation
The output relay is energized and the LED glows green
when all voltages are acceptable and the phase sequence is
correct. Under and unbalanced voltages must be sensed for a
continuous trip 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. The LED flashes red during the trip delay, then glows
red when the output de-energizes. The LED flashes green/red if
phase reversal is sensed.
Field Adjustment
Set voltage adjustment knob at the desired operating line
voltage for the equipment. This adjustment automatically sets
the undervoltage trip point. Apply power. If the PLM fails to
energize, (LED glows red) check wiring of all three phases,
voltage, and phase sequence. If phase sequence is incorrect,
the LED flashes green/red. To correct this, swap any two
line voltage connections at the mounting socket. No further
adjustment should be required.
Features & Benefits
FEATURES BENEFITS
Quick octal 8-pin
mounting
Small footprint with universal mounting: ideal
replacement for hundreds of competitive
part numbers.
Proprietary
microcontroller
based circuitry
Constant monitoring of single-phase, low voltage,
high voltage, voltage unbalance, phase reversal.
LED diagnostics
Quick visual indicator for trip versus
normal operation.
Isolated, 10A, SPDT
output contacts
Allows control of loads for AC voltages
Adjustable nominal
voltage set point
Allows setting for specific application
voltage to optimize protection
Simple 3-wire connection
for delta or wye systems
Allows flexibility across wide range of systems
ASME A17.1 Rule 210.6
Complies with safety codes for elevators,
escalators, moving walkways
NEMA MG1 14:30, 14:35
Complies with safety codes for motors
and generators
IEEE C62.41-1991 Level B
Complies with safety codes for surge and
voltage protection
Ordering Information
MODEL LINE VOLTAGE
VOLTAGE
UNBALANCE (FIXED)
TRIP DELAY (FIXED)
PLM6405 240VAC 4% 5 sec
PLM6502 240VAC 5% 2 sec
PLM6805 240VAC 8% 5 sec
PLM8405 380VAC 4% 5 sec
PLM9405 480VAC 4% 5 sec
PLM9502 480VAC 5% 2 sec
PLM9805 480VAC 8% 5 sec
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
2A fast acting fuses
recommended for safety
(not required).
Relay contacts are isolated
8-PIN
