© 2016 Littelfuse Protection Relays & Controls

www.littelfuse.com/

Rev: 1-A-062716

Protection Relays

Voltage Monitoring Relays

www.littelfuse.com/dlmu

DLMU SERIES

Description

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.

Operation

Upon application of line voltage, the output is de-energized

and the restart delay begins. If all the 3-phase voltages are

within the acceptable range, the output energizes at the end

of the restart delay. The microcontroller circuitry automatically

senses the voltage range, and selects the correct operating

frequency (50 or 60Hz). The over and undervoltage trip points

are set automatically. When the measured value of any phase

voltage exceeds the acceptable range limits (lower or upper)

the trip delay begins. At the end of the trip delay the output

relay de-energizes. If the phase voltage returns to an acceptable

value before the trip delay expires, the trip delay is reset and the

output remains energized. Under, over, and unbalanced voltages

plus over or under frequency must be sensed for the complete

trip delay before the unit trips. The unit trips in 200ms when

phase loss or reversal are sensed. The unit will not energize if a

fault is sensed as the line voltage is applied.

Reset: Reset is automatic upon correction of the voltage or

frequency fault or phase sequence.

Ordering Information

MODEL

LINE VOLTAGE

OUTPUT

RESTART FUNCTION

VOLTAGE UNBALANCE

TRIP DELAY

RESTART DELAY

DLMHBRAAA

500 to 600VAC

SPDT & NO

Staggered restart

Adjustable 2 - 10%

Adjustable 1 - 30s

Adjustable 0.6 - 300S

DLMUBLAAA

200 to 480VAC

SPDT & NO

Lockout, min off time

Adjustable 2 - 10%

Adjustable 1 - 30s

Adjustable 0.6 - 300S

DLMUBNAAN

200 to 480VAC

SPDT & NO

No restart delay

Adjustable 2 - 10%

Adjustable 1 - 30s

None

DLMUBRAAA

200 to 480VAC

SPDT & NO

Staggered restart

Adjustable 2 - 10%

Adjustable 1 - 30s

Adjustable 0.6 - 300S

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

Wiring Diagram

!

L1, L2, L3 = Line Voltage Input

NO = Normally Open Contact

NC = Normally Closed Contact

C = Common,Transfer Contact

CAUTION: 2 amp max. fast acting fuses are

recommended to protect the equipment‘s wiring.

They are not required to protect the DLMU.

! = Select alarm contact connection as N.O. or N.C. when ordering;

N.O. Shown.

Features & Benefits

FEATURES

BENEFITS

Proprietary

microcontroller

based circuitry

Constant monitoring to protect against phase loss,

phase reversal, over voltage, under voltage,

unbalance, short cycling and over/under frequency

Universal line

voltage range

Flexibility to work in 200 to 480VAC or 500 to

600VAC applications

DIN rail (35mm) or

surface mounting

Installation flexibility

LED indication

Provides diagnostics of relay, fault and time

delay status

User adjustable

time delays

Prevents nuisance tripping and short cycling of

sensitive equipment