What this MCCB is and what it does
The Siemens 3VA1125-3EF32-0HA0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection in distribution panels and industrial switchgear. It carries a rated current of 25 A at 40 °C ambient, with a thermal-magnetic overcurrent release (TM240) that provides both overload and short-circuit protection in a single trip unit. The 3-pole construction handles three-phase circuits, and the interrupting capacity is rated per IEC/UL at 75.6 kA at 240 V AC, 52.5 kA at 415 V, and 11.9 kA at 690 V — figures that determine the available fault current the breaker can safely clear without upstream coordination failure. A built-in shunt trip release (STL) allows remote tripping via a control voltage signal, which is useful for emergency-stop circuits or supervisory shutdown sequences. The rated insulation voltage is 800 V, matching the voltage class of typical 690 V industrial networks.
Thermal derating and operating range
The 25 A rating holds from 40 °C through 50 °C ambient. Above that, the breaker derates linearly: 24 A at 55 °C and 60 °C, then 23 A at 65 °C and 70 °C. This matters for panels mounted near heat sources or in non-air-conditioned enclosures — the actual continuous current the breaker can carry is the derated value at the panel's internal temperature, not the nameplate 25 A. Operating ambient range is -25 °C to +70 °C, with storage from -40 °C to +80 °C. Maximum power loss at rated current is 8.5 W per pole, which adds to the enclosure's thermal budget and should be factored into the panel cooling calculation.
Physical fit and panel integration
Dimensions are 76.2 mm wide, 130 mm tall, and 70 mm deep — a standard 3-pole MCCB footprint that mounts on a DIN rail or directly to a backplate via the breaker's mounting base. The 70 mm depth (2.76 in) is the dimension from the mounting surface to the front of the breaker, which determines the minimum enclosure depth required for wiring clearance.