MPU-32 Series

Motor Protection Unit

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The MPU-32 Motor Protection Unit is used to provide currentand temperature-based protection, metering, and data logging for three-phase low-voltage medium-horsepower induction motors. This relay is ideal for retrofitting and upgrading obsolete or aging motor protection using existing CTs. See the PMA Family of Panel Mount Adapter Kits to replace common obsolete relays.

Motor Protection Unit

  • Three ac-current inputs
  • Earth-leakage-CT input
  • Programmable digital input
  • 24-Vdc source for digital input
  • Programmable 4-20-mA analog output
  • On-board temperature-sensor input,
  • 100-Ω-Platinum RTD or PTC 
  • Three programmable output relays
  • Local RS-232 communications, optional Network Communications
  • PC-interface software (SE-Comm-RIS)
  • 4 line x 20 character backlit LCD display
  • Keypad for programming and display selection
  • 4 LEDs; 1 user programmable

Current Input Module (MPU-CIM)

The MPU-CIM Current Input Module is the interface between the MPU-32 relay and the 5-A-secondary, 1-A-secondary, and sensitive current transformers. The MPU-CIM is ordered separately from the MPU-32 and can be surface- or DIN-rail mounted. Wire-clamping terminals are standard but the MPUCTI is available for those who require ring-tongue terminals.

Features & Benefits

  • Overload

    Extends motor life and prevents insulation failures and fires

  • Dynamic thermal model

    Provides protection through starting, running, and cooling cycles

  • Communications

    Remotely view measured values and event records, reset trips, and access setpoints

  • Ground fault

    Prevents catastrophic failures and fires

  • Current unbalance/Phase loss/Phase reverse

    Prevents overheating due to unbalanced phases

  • RTD temperature

    RTD temperature protection (MPS-RTD module) for high-ambient or loss-of-ventilation protection

  • Phase loss/Phase reverse (current)

    Detects unhealthy supply conditions

  • Overcurrent

    Prevents catastrophic failures and fires; extends motor life

  • Jam

    Prevents motor damage by detecting mechanical jams or excessive loading

  • Undercurrent

    Detects low level or no-load conditions

  • PTC overtemperature

    Overtemperature (PTC) protection for high-ambient or loss-of-ventilation detection

  • Starts per hour

    Limits the motor starts per hour to prevent overheating

  • Differential

    Optional MPS-DIF module for sensitive winding-fault protection

  • Reduced overcurrent mode

    Minimizes arc-flash hazards during maintenance

  • Metering

    View measured and calculated parameters with on-board display


    Separate current input module to reduce risk of open-CT hazard and for convenient installation

  • Analog output

    Provides means for metering selectable parameters

  • Data logging

    On-board 100-event recorder for data logging

  • Conformal coating

    Internal circuits are conformally coated to protect against corrosion and moisture

MPU-32 Datasheet

MPU-32 Manual

MPU-32 DeviceMet Manual


  • Protective Functions (IEEE Device Numbers): Overload (49, 51), RTD temperature (38, 49) Phase reverse (current) (46), Overcurrent (50, 51), Jam, Ground fault (50G/N, 51G/N), PTC overtemperature (49, Unbalance (current) (46), Starts per hour (66), Differential (87), Phase loss (current) (46), Undercurrent (37)
  • Input Voltage: 65-265 Vac, 25 VA; 80-275 Vdc, 25 W
  • Power-Up Time: 800 ms at 120 Vac
  • Ride-Through Time: 100 ms minimum
  • 24-Vdc Source: 100 mA maximum
  • AC Measurements: True RMS and DFT, Peak, 16 samples/cycle, and positive and negative sequence of fundamental
  • Frequency: 50, 60 Hz or ASD
  • Output Contacts: Three Form C programmables
  • Communications: TIA-232 (standard); TIA-485, DeviceNet™, Ethernet (optional)
  • Analog Output: 4-20 mA, programmable
  • Conformally Coated: Standard feature
  • Warranty: 10 years
  • Mounting (Control Unit): Panel (standard) Surface (with MPU-32-SMK converter kit)(Current Input Module) DIN, Surface
  • Approvals: CSA certified, CE (European Union), UL Recognized, C-Tick (Australian)

Ordering Information



TIA-232 & TIA-485
TIA-232 & DeviceNet™
TIA-232 & EtherNet/IP™ & Modbus® TCP


Phase CTs


Phase Current Transformers
Phase CTs are required to detect phase currents. For upgrade applications, existing CTs can be used.

Ground-Fault Current Transformer
Optional zero-sequence current transformer detects ground-fault current. Available with 5-A and 30-A primary ratings for low-level pickup.

MPS-RTD Temperature Input Module
Optional module provides 8 inputs to connect Pt100, Ni100, Ni120, and Cu10 RTDs.

MPS-DIF Differential Current Module
Optional motor differential protection, compatible with core balance and summation current transformer connections.

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Featured Case Study

Smart Relay Creates Safety & Efficiency Boom

A large oil & gas exploration company made what is expected to be one of the biggest oil and gas discoveries of the decade in the Permian region’s western part of Texas. The company began evaluating several brands of protection relays to protect their investments in pumps and motors, optimise productivity, and improve safety. After the company’s engineers tried the Littelfuse Bluetooth® Overload Relay MP8000, the search was over.

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Top FAQs

The MP8000 has a wide voltage and current range and operates on 50/60 Hz to protect any motor or pump.

It can also be used to retrofit older current-only based electronic overloads.

It can operate between 90-690VAC and 0.5-1,000A.

Traditional relays require the user to open the electrical cabinets (where relays are typically installed) panel door to use the relay, whether it’s to modify the settings, or to review the cause of a trip event. 

Opening the panel door exposes the worker to shock hazards. Bluetooth, however, enables remote access to these settings, metering and data log information which prevents personnel from unnecessarily having to open the door, thus less exposure to risks.

  • Overload (Overpower) (49)
  • Underload (Underpower) (37P)
  • Overcurrent (51)/Jam
  • Undercurrent (37)
  • Current Unbalance/Phase Loss (46)
  • Phase Reversal (47)
  • Overvoltage (59)
  • Undervoltage (27)
  • Voltage Unbalance (47)
  • Rapid Cycling/Jog
  • Contactor Failure
  • Zero-Sequence Ground Fault (50Ns)
  • PTC Motor Overtemperature (49)

The MP8000 can be used in both single phase and 3 phase applications.

Yes, the MP8000 can be put into current-only mode which will disable voltage-based protection functions. However, Littelfuse strongly recommends utilizing the voltage-based protection functions for superior protection especially prior to motor startup.

The current-only mode is intended for retrofit applications on voltages above 690 VAC.

The MP8000 can be surface or panel mounted, or installed on a DIN rail.

No, the MP8000 uses Bluetooth to connect to your smart phone or tablet via the Littelfuse app, This enhances the users safety as it allows remote access.

Yes, you can access the information remotely through the Littelfuse MP8000 PC software or through other software programs communicating with the MP8000 through the Ethernet interface. Contact Fuseco for information on how to download this software.

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Applicable Industries

Hi Tim, just wanted to thank you and the Fuseco team for your help. You've managed to help us solve some nagging issues here and the Littelfuse SE-330AU relay installation has saved us a lot of time. Thanks!

Mark Sherman

PGS Silver, Queensland

Just wanted to send a note of thanks to you guys. When it comes to relays, your advice & service is high level & appreciated. Cheers.

Jesse Marshall

Newcrest WA

The Littelfuse SE-701 & the CT's are functioning well. Thanks guys, really appreciate your help. Good to work with people you can rely on.

Cliff Peligro

Alpha Coal, Queensland

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