AC-PRO-MP® Approved
Merlin Gerin Masterpact M Tripping Solutions
STR Nuisance Tripping Solved
AC-Pro-MP can be fitted quickly and efficiently by our accredited engineers
Masterpact Tripping Solutions
Is your Merlin Gerin Masterpact M ACB Nuisance Tripping?

Utility Relay Company AC-PRO-MP®

The AC-PRO-MP® (also known as URC Amp-Safe-Pro) is a direct replacement trip unit for the STR trip units on the Schneider / Merlin Gerin Masterpact M, MP, IEC, UL and Square D breakers. Often re-badged as the Moeller IZM (which is identical to the Masterpact M).

The AC-PRO-MP® does not use rating plugs and is user programmable to replace any versions of the STR 18M, 28D, 38S, 58U. It has the same protective functions, settings and time-current-curves as the original STR units; long time, short time, instantaneous over current and ground fault.

By fitment of these units Switchserve helps our many clients’ facilities eliminate nuisance tripping. This enables an upgrade to a mechanically sound ACB (as opposed to changing the entire breaker), and resumes power both quickly and efficiently after an STR unit has failed, by having Amp-Safe-Pro units in stock and ready to fit.  These units are an ideal solution in scenarios where power is unable to be reinstated with a faulty STR unit. This will ensure that an existing good condition Merlin Gerin Masterpact breaker is updated to prevent costly and disruptive downtime.


The AC-PRO-MP® trip unit can be fitted effectively in a short space of time and uses the same style plug type and format as the original equipment. Our qualified engineers can have the new unit fitted, set up, secondary injection tested and power restored in approximately 30 minutes!

The AC-PRO-MP® trip unit offers today’s levels of set up options and can give more adjustment and function than the STR unit it replaces, such as trip history and load monitoring.  Once fitted to a Masterpact (or Moeller XZM/Square D branded) air circuit breaker, the trip unit is secondary injection tested with the U.R.C (Utility Relay Company) test set across each phase individually as well as ground fault if fitted; proving the protection on all available parameters.

The AC-PRO-MP® also benefits from being adaptable to different frame sizes (3 or 4 pole) and is able to be rated to suit any Masterpact breaker. As a the rating can also be programmed the unit can also then be moved and used on another breaker if required. Another advantage is its compatibility with neutral sensors in residual ground fault protection schemes.  CE approval also ensures the AC-PRO-MP® trip unit adheres to all EU requirements.

Availability & Lead Time

Switchserve can usually supply, install, set-up and test AC-PRO-MP® trip units with immediate effect, as we carry a maintained stock level at all times. The unit can be programmed exactly to the settings of your old STR, with the added compliment of being programmable via its front panel control buttons and including an LCD display for viewing both settings and trip events. It can also give a “live” display showing current per phase for monitoring and pick up indication.

For further information or technical advice regarding STR problems and AC-PRO-MP® trip units, you can contact us here.