Masterpact M trip unit: AMP-SAFE PRO

The Masterpact M circuit breaker has an installed base running into tens of thousands. However, since factory support was discontinued in 2014, thousands of users have been left without a source for replacement trip units.

The AMP-SAFE PRO solves that problem.

The AMP-SAFE PRO is the only UL and CE-listed replacement for STR breaker protection units and is a direct replacement for a Merlin Gerin Masterpact M trip unit (breaker protection unit). It extends the serviceable life of a circuit breaker without the expense or downtime associated with a full refurbishment.

The AMP-SAFE PRO directly replaces the Schneider Electric trip unit in Masterpact M circuit breakers

The AMP-SAFE PRO directly replaces the Schneider Electric trip unit in Masterpact M circuit breakers

Direct replacement for the Masterpact M

Since discontinuing the Masterpact M, Schneider Electric has promoted the idea of an entirely new circuit breaker when existing trip units fail. This is expensive, disruptive and also unnecessary. Just 20 minutes is all that’s needed to restore a circuit breaker to full working condition with the AMP-SAFE PRO. Apart from the obvious savings in time and money, the AMP-SAFE PRO offers numerous advantages:

  • Compatibility: the AMP-SAFE PRO trip unit is compatible with Merlin Gerin & Square D Masterpact M IEC and UL-rated circuit breakers as well as Klockner Moeller IZM models that use a XZMA type protection unit.
  • Programmability: the AMP-SAFE PRO trip unit is user-programmed to replace STR-18M, 28D, 38S or 58U trip units.
  • Technical accuracy: the AMP-SAFE PRO trip unit has the same protective functions, settings and time-current curves as the original STR.

What are the main features of the AMP-SAFE PRO?

  • User programmed to replace any of the versions of STR-18M, 28D, 38S or 58U trip units on IEC or UL rated
    Masterpact MP breakers.
  • Standard Trip Functions (based on the STR-type entered): long-time / phase and neutral over-current; short-time; instantaneous; residual ground fault; ground return fault; instantaneous on closing (DNF); over-temperature trip
  • A security code system protects against unauthorized changes to the settings.
  • Includes the exact trip unit functions, settings and time current-curves as the original STR trip unit.
  • It Includes the same information and alarm features as the original STR trip unit.
  • No physical rating plug is required because the rating plug value is a programmed setting.
  • Includes the Quick-Trip arc flash reduction settings with an On/Off switch and LED on the front of the breaker protection unit (trip unit) as a standard feature.
  • Remote Quick-Trip On/Off switch as well as indication light are optional.
  • Easy access to the settings and data is provided with an OLED graphic display and “smart” push buttons.
  • Standard Information & Alarm Functions: 2 Load monitoring settings with output contacts; pre-trip alarm contact & LED indicator; breaker tripped alarm output contact is programmed by type of trip; and stamped trip events.
  • Easy to read OLED display.
  • A USB port on the front of the trip unit provides for connection to a laptop computer for easy access to the settings and last trip data.
  • A test port for connection to a secondary injection test set that performs actual Phase and Ground Fault tests, instead of not simulated tests.
  • SELF-TEST Features: continuously monitors the actuator connection; proper execution of the software routines; the micro-controller and A/D converters.
  • Last Trip Data: the last trip data is saved for 8 trips and includes the type of trip, phase and ground currents as well as the time and date of each trip. The trip counter provides the number of trips by trip function.


The AMP-SAFE-PROTM is independent laboratory tested and is compliant with:

  • ANSI/IEEE C37.90.2-2004, RF Susceptibility.
  • ANSI/IEEE C37.90.1-2002, Surge Withstand.
  • and EN61000-4-2 Electro-Static Discharge.

The AMP-SAFE-PROTM is UL and ULC classified and passed ANSI C37.59 testing on a Merlin Gerin 16MP-H1 breaker.

The AMP-SAFE-PROTM is tested to EN60947-2 so has the CE mark.



The AMP-SAFE-PRO-PLUS is identical to the Amp-Safe-Pro, with the additional feature of wireless or wired RS485 communications.