What this MCCB is and what it carries
The Siemens SENTRON 3VA1112-4FE42-0AA0 is a 4-pole molded case circuit breaker (MCCB) designed for line protection. Rated at 125 A at 40 °C, it uses a TM220 thermal-magnetic overcurrent release — the thermal element handles overloads, the magnetic element handles short-circuits. The 125 A rating is the continuous current it can carry without tripping at that ambient; above 55 °C it derates to 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C, so if this breaker lives in a hot panel or near other heat sources, you need to account for that drop.
Breaking capacity — what it interrupts
Breaking capacity is the real selector here. At 240 V it interrupts 121 kA — that's a very high fault-current rating for a 125 A frame, meaning it can sit on a transformer secondary or a high-capacity bus without needing a current-limiting fuse upstream. At 415 V it's 75.6 kA, at 440 V it's 52.5 kA, and at 500 V and 690 V it drops to 11.9 kA. If your system voltage is 480 V or higher, that 11.9 kA figure is the one that governs your SCCR coordination study.
Physical fit and panel integration
Dimensions: 70 mm deep, 101.6 mm wide, 130 mm tall. The front face carries an IP40 rating.