Products > AC-PRO-MP & AC-PRO-MP-II

AC-PRO-MP® and AC-PRO-MP-II®, Masterpact Direct Replacement

The AC-PRO-MP & AC-PRO-MP-II are plug-in, direct replacement trip unit for Merlin Gerin, Schneider Electric Masterpact MP, & Klockner Moeller IZM, IEC, or UL rated Breakers.
The AC-PRO-MP & AC-PRO-MP-II do not use rating plugs and are user programmable to replace any versions of the STR 18M, 28D, 38S, 58U.

The AC-PRO-MP & AC-PRO-MP-II have the same protective functions, settings and time-current-curves as the original STR units.

AC-PRO-MP-II Additional Features:

  • Voltage Metering (line-to-line) rated for up to 600V three-phase systems
  • Power and energy metering (KW, KVA, KWHrs, Power Factor)
  • Modbus RTU communications via RS-485 network
  • UL and CE Certification

    To ensure that the AC-PRO-MP & AC-PRO-MP-II will function when needed the AC-PRO-MP was tested to the ANSI C37.59 Standards for fault interruption. As a result of this testing the AC-PRO-MP & AC-PRO-MP-II are UL certified. This makes the AC-PRO-MP & AC-PRO-MP-II the only Masterpact replacement trip units that are UL listed.

    The AC-PRO-MP & AC-PRO-MP-II also carry the CE mark.



    AC-PRO-MP, Masterpact Direct & Merling Grein Replacement Trip UnitAC-PRO-MP, Masterpact Direct & Merling Grein Replacement Trip UnitStandard trip functions include:

    (These will vary depending on the STR type selected)

    • Long-Time
    • Short-Time
    • Instantaneous
    • Residual Ground Fault
    • Ground Return Ground Fault
    • Instantaneous on Closing
    • Over Temperature Trip

    All of the settings are protected by a security code to prevent unauthorized modifications.

    Additional Functions:

    Sluggish Breaker Detection

    The AC-PRO-MP & AC-PRO-MP-II now have the ability to detect if the Masterpact breaker mechanism needs service. The first time a breaker opens after a long period of inactivity it may open slowly. This can be caused by mechanical issues, poor lubricant or other obstructions.
    The AC-PRO-MP & AC-PRO-MP-II will capture the sluggish breaker event and display a warning on the screen the next time it is powered up. An external alarm can also be activated when the
    AC-PRO-MP & AC-PRO-MP-II detect a sluggish breaker event.

    When the breaker has detected a sluggish opening it will show this alert the next time the AC-PRO-MP &
    AC-PRO-MP-II is turned on.
    After the initial warning you can view the actual clearing time.

    USB Port

    The front mounted and electrically isolated USB port allows for easy downloading of trip data and protection settings. It can also be used to upload the trip unit settings, making commissioning the trip unit much faster. The USB port can also be used with the SAFE-T-TRIP system.

    InfoPro-MP Software compatible

    InfoPro-MP is a software application that can be used with AC-PRO-MP units that shipped prior to December 2016. It offers the following capabilities:

    • Settings – upload, download, view, and save
    • Trip unit info: serial number, firmware versions, breaker name
    • Firmware updates
    InfoPro-MP-II software is for MP & MP II units that shipped in December 2016 or later (these units can easily be identified by their front test port). In addition to the above features, InfoPro-MP-II includes the following:

    • Waveform capture (on-demand and for the last 8 trips)
    • Current readings
    • Voltage, power, & energy readings (AC-PRO-MP-II only)


    The AC-PRO-MP & AC-PRO-MP-II can be programmed one of two ways.  The front of the unit has an OLED display that is easy to read in either low or high ambient light.  The buttons on the front of the unit are “smart” buttons that change their functions based on the displayed information.  The second way to program the AC-PRO-MP & AC-PRO-MP-II is using the USB port on the front to connect to the InfoPro-MP software application, which is supplied by URC. The program makes it very easy to commission the AC-PRO-MP & AC-PRO-MP-II.  InfoPro-MP can also be used to view historical data, upgrade the firmware, save the commissioning data and reload the AC-PRO-MP from a saved file.  


    The AC-PRO-MP & AC-PRO-MP-II are also compatible with Utility Relay Company's SAFE-T-TRIP which provides a means for an operator to safely trip a breaker without having to stand directly in front of the switchgear.




    AC-PRO-MP installed on a Masterpact Breaker
    The AC-PRO-MP & AC-PRO-MP-II have a mechanical pop out trip indicator on the front of the unit that mimics the functionality of the original unit.  There is also a SELF-TEST OK Led, PRE-TRIP LED, QUICK-TRIP switch and an easily accessible LI-Ion battery. The SELF-TEST OK LED indicates a properly operating trip unit. The PRE-TRIP LED indicates a pending trip.  The QUICK-TRIP switch activates QT-Instantaneous and QT-Ground Fault settings in the trip unit to reduce arc flash hazard. 

    The battery in the AC-PRO-MP & AC-PRO-MP-II is only used to power the trip unit to review trip data or change settings when no power is provided from the CT’s.  The battery is not used for any of the protective functions of the AC-PRO-MP & AC-PRO-MP-II.  The battery is also not used to save the last trip data or settings.  All of this data is saved in non-volatile memory.  The trip unit saves the type of trip, phase, waveforms, ground currents and date/time for the last 8 trip events.  There is also a trip counter that provides the number of trips by trip function.

    Online Ordering

    Please visit our Kit Ordering Guide page and use the interactive online ordering system to order an AC-PRO-MP & MP-II to replace your faulty Masterpact unit. You can also Contact Us if you need assistance

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    Product Information

    Product Fliers

    AC-PRO-MP Product Flier

    Instruction Manuals

    AC-PRO-MP & AC-PRO-MP-II Instruction Manual

    AC-PRO-MP Secondary Injection Test Set Manual


    InfoPro-MP, AC-PRO-MP Software Application

    InfoPro-MP-II, AC-PRO-MP & AC-PRO-MP-II Software Application



    AC-PRO-MP Installation