What it is and what it does
The Siemens SENTRON 3VA1112-6MH32-0AA0 is a 3-pole molded case circuit breaker (MCCB) rated 125 A continuous at 40 °C, designed specifically for starter protection — meaning it's built to coordinate with motor starters and protect the branch circuit feeding a motor load. The overcurrent release is a TM120M thermal-magnetic unit, so the thermal element handles overloads and the magnetic element clears short circuits without relying on external trip electronics — no undervoltage release, no ground-fault monitoring, no communication function on this variant.
Breaking capacity — what the numbers mean for coordination
This breaker delivers 220 kA at 240 V, 154 kA at 415 V, and 75.6 kA at 440 V — numbers that put it in the high-interrupting category for a 125 A frame. At 500 V and 690 V it still holds 7.5 kA, which is useful for industrial systems with higher fault currents upstream. The 220 kA at 240 V means it can sit directly behind a large transformer without needing a current-limiting fuse ahead of it — the breaker itself clears the fault. That saves panel space and a fuse holder.
Thermal derating and temperature range
Rated 125 A from 40 °C up to 50 °C, then derates to 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C. If your panel ambient runs above 50 °C, you lose about 1 A per 5 °C — plan the load accordingly. Operating ambient range is -25 °C to 70 °C; storage range is -40 °C to 80 °C. The storage limit is wider because the breaker isn't carrying current — that's the handling limit, not the running limit.
Physical fit and panel integration
Dimensions: 130 mm high, 76.2 mm wide, 70 mm deep. The 76.2 mm width is a standard 3-inch footprint for a 3-pole MCCB in this class — it fits common panel cutouts and busbar layouts. Power loss is 28.1 W maximum at rated current — that's the heat you need to vent from the enclosure. For a sealed panel, factor that into the thermal calculation.