The Siemens 3VA1112-5MH32-0AA0 is a SENTRON molded case circuit breaker (MCCB) designed for starter protection — meaning it's built to handle the high inrush and overload profile of motor circuits, not just general distribution. It carries a 125 A rating at 40 °C with a TM120M thermal-magnetic trip unit, so the thermal element tracks motor heating while the magnetic element clears short circuits fast. Breaking capacity reaches 187 kA at 240 V, dropping to 121 kA at 415 V and 75.6 kA at 440 V — numbers that matter when you're coordinating downstream with a motor starter and need the MCCB to take the full fault without upstream interruption.
Current derating and thermal budget
This breaker holds its full 125 A rating up to 50 °C ambient. Above that, it derates linearly: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C. If the panel runs hot — say, near the 70 °C operating maximum — you lose about 9 % of the continuous current capacity. The maximum power loss is 28.1 W, which is the heat the breaker dumps into the enclosure; factor that into your panel thermal calculation, especially in a sealed cabinet.
Panel fit and protection class
The breaker measures 70 mm deep by 76.2 mm wide by 130 mm tall — a standard 3-pole MCCB footprint that fits most DIN-rail or panel-mount enclosures without surprises. Front protection is IP40, so it's sealed against tools and small solids but not against water ingress; keep it inside a rated enclosure in washdown areas. Rated insulation voltage is 800 V, giving headroom for 480 V and 600 V class systems. Operating temperature range is -25 °C to 70 °C, storage from -40 °C to 80 °C.