DLMHBRAAA - DLMU Series

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Littelfuse Voltage Monitoring Relays
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The DLMU Series is a universal voltage, 3-phase voltage monitor. It continuously measures the voltage of each of the three phases with microcontroller accuracy and compares the value to preset trip points. It separately senses phase reversal and loss; over, under and unbalanced voltages; and over or under frequency. Protection is assured during periods of large average voltage fluctuations or when regenerated voltages are present. The unit trips within 200ms when phase loss is detected. Adjustable time delays are included to prevent nuisance tripping and short cycling of sensitive equipment. The isolated, 10A, SPDT and 2A alarm output relay contacts trip when a phase voltage exceeds the trip limits for the trip delay. Nominal line voltage, voltage unbalance, and time delays are knob adjustable. The phase loss setpoint and the acceptable frequency range are fixed. Both delta and wye systems can be monitored; no connection to neutral is required.


See datasheet for operation details.

Property (Mouseover for details) Value
Input Voltage (V) 500-600VAC
Input Voltage Maximum (V) 600VAC
Input Type 3-phase delta or wye with no connection to neutral
Input AC Line Frequency (Hz) 50/60Hz
Input Phase Sequence A B C L1 L2 L3
Output Type Isolated electromechanical relay
Output Load Rating (VA) 10A resistive @ 240VAC; 8A resistive @ 277VAC; NO-1/4hp @ 120VAC; 1/3hp @ 240VAC
Reset Time (ms) Automatic
Response Time (ms) Phase loss: ≅200ms; Phase reversal: ≅200ms
Restart Delay Range Adjustable from 0.6-300s
Restart Delay Tolerance (%) ±15%
Trip Delay Type Active On: Over/undervoltage voltage unbalance over/under frequency
Trip Delay Range Adjustable from 1-30s
Trip Delay Tolerance (%) ±15%
Overvoltage Trip Voltage (%) 109-113% of the adjusted line voltage
Overvoltage Reset Voltage (%) ≅-3% of the trip voltage
Undervoltage Trip Voltage 88-92% of the adjusted line voltage
Undervoltage Reset Voltage (%) ≅+3% of the trip voltage
Voltage Unbalance Trip Point (%) Adjustable 2-10%
Voltage Unbalance Reset (%) ≅-0.7% unbalance
Over/Under Frequency (%) ±4%; Reset ±3%; 50/60Hz
Phase Loss ≥25% unbalance
Isolation Voltage (V) ≥2500V RMS input to output
Surge Protection IEEE C62.41-1991 Level B
Type of Detection Voltage detection with delayed trip and automatic reset
Life Mechanical - 1 x 106; Electrical - 1 x 303
Termination Type Screw terminal with captive wire clamps for up to #14 AWG (2.5mm2) wire
Mounting Method Surface mount with two #8 (M4 x 0.7) screws or snap on 35mm DIN rail
Operating Temperature -40° to 60°C (-40°F to 140°F)
Storage Temperature (F/C) -40° to 85°C (-40°F to 185°F)
Humidity 95% relative non-condensing
Dimensions 4.33 x 2.95 x 1.97 in. (110 x 75 x 50mm)
Weight (lbs/g) ≅8.6oz (244g)