Guide · Schneider / Merlin Gerin Masterpact M
Masterpact M end of life: repair or replace?
The Masterpact M went out of production in 2003. Many are still carrying load in US switchboards. When one fails, you have two real options: the OEM retrofit or a repair of the breaker you already own. Here is how they compare.
What "end of life" means for a Masterpact M
The Merlin Gerin Masterpact M covers frames M08 to M63, with STR electronic trip units (STR28D, STR38S and STR58U are the common ones). Schneider declared the range obsolete on October 1, 2003, and replaced it with Masterpact NT and NW, and later MTZ.
Schneider's own retrofit literature says spare parts stayed available on a limited basis for about ten years after that, and that availability has not been guaranteed since 2013. In practice, that means no new STR trip units, no new mechanisms and a shrinking supply of coils and motors from the manufacturer.
"Obsolete" is a commercial status. It tells you the OEM will no longer build or support the breaker. It does not tell you the breaker is worn out. The frame, the poles and the mechanism of a Masterpact M are robust, and most failures we see are in parts that can be rebuilt.
What usually fails
A Masterpact M is now at least 20 years old, and often much older. The faults follow age:
- STR trip unit electronics. Nuisance tripping, a dead unit, or a unit that fails a secondary injection test. On an M, a trip unit that trips for no reason is usually end-of-life electronics.
- Hardened mechanism grease. The breaker closes slowly, hesitates, or will not latch.
- Closing coil and charging motor. The motor brushes and gearbox wear; the closing coil fails.
- Main and arcing contacts. Erosion on breakers that have cleared faults or switched often.
- Cradle cluster contacts on drawout units: heat at the stabs on a thermal survey points to eroded or loose clusters.
Option 1: the OEM route, an MTZ in the old chassis
Schneider's answer to a failed Masterpact M is ECOFIT. The plug-and-play version puts a new Masterpact MTZ breaker, with a Micrologic X control unit, into the existing Masterpact M chassis. According to Schneider's documentation it covers drawout breakers only, 3-pole and 4-pole, from 800 A to 3200 A. On site, the drawer side plates and the auxiliary wiring connector plate are replaced; the busbars and cables stay as they are.
Fixed breakers and the larger frames need a different solution, with more work on the switchboard.
The retrofit gives you a current-generation breaker with full OEM support and modern protection and metering. Those are real benefits. The costs are also real:
- A new breaker at new-breaker prices, often for every M in the board if you want one standard.
- OEM lead times for the breaker and the kit.
- Secondary wiring changes, new settings and a commissioning visit.
- A protection coordination check, because the Micrologic X curves are not the STR curves.
Option 2: repair the original breaker
A workshop repair keeps the breaker you have, in the cell it was built for. A full repair on a Masterpact M includes:
- Mechanism: stripped, every part cleaned, worn pins and links replaced, re-lubricated with the correct grade and proved through the charge, close and open sequence.
- Contacts: main and arcing contacts inspected against wear limits and renewed as sets where needed; arc chutes inspected.
- Coils and motor: closing coil and charging motor replaced or rebuilt.
- Trip unit: the STR tested by secondary injection. If it fails, the options are a tested STR from donor stock where one exists, or an ETC-12Q or AC-PRO replacement trip unit fitted inside the original frame and set to reproduce the STR characteristic.
Because Schneider no longer supplies M parts, they come from donor breakers, from parts re-machined to pattern, and from engineered modern equivalents for coils, motors and trip units. The certificate says which.
Every repaired breaker is secondary-injection tested across its protection elements at your settings, with contact resistance per pole and insulation resistance recorded. It ships back with the certificate, before and after photos and a parts list. See a sample certificate.
How to decide
Repair usually makes sense when
- The switchboard is sound and you want it to stay as designed and approved.
- One or two breakers have failed and the rest of the board is working.
- You need the breaker back quickly and cannot wait for an OEM retrofit lead time.
- You want to keep the existing protection settings and coordination study valid.
- The breaker is fixed-mounted or outside the plug-and-play rating range.
The retrofit usually makes sense when
- You are planning a board upgrade anyway, with an outage and a budget.
- You need metering or communications that the STR units cannot give you.
- Your site standards require current-production breakers with OEM support.
- The breaker has damage that is not economic to repair. We will tell you if that is the case.
The two options are not exclusive. You can repair now to restore service and plan a retrofit for a later outage. A repaired breaker can also be held as a tested spare once the board is upgraded.
What to send us
A first answer only needs photos and a few details:
- A photo of the nameplate: frame (M08 to M63), breaking class, rating, 3-pole or 4-pole, fixed or drawout.
- A photo of the trip unit and its rating plug, and the current settings if you can read them.
- What happened: will not close, will not charge, nuisance tripping, failed test, or damage after a fault.
- Whether the cradle comes too, and the control voltage for the coils and motor.
- How many units you have, and how urgent the job is.
We reply the same working day. The breaker flies to our UK workshop in about 3 days, is stripped and quoted at a fixed price before any repair, and comes back by air. Door to door is typically about 8–11 working days plus customs clearance, or about 7–8 on Express. You choose DAP or DDP, and we prepare the commercial invoice and repair-and-return paperwork. Repairs carry a 12-month warranty; full overhauls carry 24 months.
Frequently asked questions
Is the Masterpact M still supported by Schneider?
No. Schneider declared the Masterpact M obsolete on October 1, 2003, and its retrofit literature says spare parts have not been guaranteed since 2013. The OEM route today is a retrofit, such as ECOFIT with an MTZ breaker in the old chassis.
Can a failed STR trip unit be replaced?
Yes. Where a tested STR is available from donor stock, it can be fitted. Otherwise an ETC-12Q or AC-PRO replacement trip unit is fitted inside the original frame and set to reproduce the STR characteristic, then proved by secondary injection at your settings.
Does the ECOFIT plug-and-play retrofit work on every Masterpact M?
No. Schneider's documentation limits the plug-and-play version to drawout breakers, 3-pole and 4-pole, from 800 A to 3200 A. Fixed breakers and larger frames need a different solution with more work on the switchboard.
Will a repaired Masterpact M go back into its own cradle?
Yes. The repair keeps the original frame, so the breaker racks back into its own cell with the same busbar connections and secondary wiring.
What if the breaker is not worth repairing?
The breaker is stripped and inspected before any repair is priced. If the damage makes repair uneconomic, we say so before any repair work starts.
More on the range, the faults we see and how each unit is tested is on our Masterpact M repair page. To start, send the nameplate and the fault through request a quote.
Send us the nameplate
A photo of the nameplate and the fault is enough for a first answer. We reply the same working day with a recommendation and a price for diagnosis and freight.