What it is and what it does
The Siemens 3VA1125-4GF42-0AA0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection in distribution panels. It carries a continuous rating of 25 A across four poles, with a TM240 thermal-magnetic overcurrent release that handles both overload and short-circuit conditions without an external trip unit.
Interrupting capacity — what the numbers mean for your panel
The interrupting ratings tell you where this breaker can safely clear a fault without welding or rupturing. At 240 V it's rated 121 kA, which covers most North American secondary-side faults. At 415 V it handles 75.6 kA, and at 440 V it's 52.5 kA — both figures that suit European and Asian industrial supply points. Above that, at 500 V and 690 V, the rating drops to 11.9 kA, so you'll need to verify the available fault current at the installation point if you're feeding a 690 V motor control center.
Thermal derating and operating range
The breaker holds its full 25 A rating from 40 °C up to 50 °C ambient. At 55 °C it derates to 24 A, and at 70 °C it's 23 A. That's a shallow derating curve — useful if the panel runs warm or sits near other heat sources. The operating ambient range is -25 °C to 70 °C, with storage from -40 °C to 80 °C. Front face protection is IP40, so it's fine for indoor panel mounting but not for washdown areas.
Physical fit and panel integration
Dimensions are 130 mm high, 101.6 mm wide, and 70 mm deep. The 70 mm depth is shallow enough for most standard-depth enclosures without gland-plate interference. Four-pole width at 101.6 mm matches the typical 4-pole MCCB footprint on a DIN rail or mounting plate.