What it is and what it does
The Siemens SENTRON 3VA1112-6MH36-0BC0 is a 3-pole molded case circuit breaker (MCCB) rated for 125 A continuous current at 40 °C ambient, with a breaking capacity of 220 kA at 240 V AC and 154 kA at 415 V AC. It is designed specifically for starter protection — meaning it's built to handle the high inrush and short-circuit stresses of motor-starting applications, not just general distribution. The breaker includes an integrated undervoltage release (UVR) and two auxiliary switches (HQ design), so it can be wired into safety circuits or remote status monitoring without adding external accessories.
What the ratings mean for fit
The 125 A rating holds flat from 40 °C to 50 °C, then derates gradually: 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, this breaker still delivers over 90 % of its nameplate — useful for a cramped enclosure without forced ventilation. The 800 V rated insulation voltage (Ui) means it's safe for 690 V line-to-line systems, and the 7.5 kA breaking capacity at 690 V confirms it can clear a fault on a 690 V motor circuit, though at a much lower level than the 240 V or 415 V ratings. Power dissipation is 30.6 W maximum — not negligible in a sealed panel. If you're packing multiple breakers in a row, factor that heat into the enclosure sizing or add a vent.
Where it goes and how it mounts
This MCCB mounts on a DIN rail (standard 35 mm profile) or can be screw-fixed to a backplate. Dimensions are 130 mm height, 76.2 mm width, and 70 mm depth — a 3-pole footprint that fits most panel layouts without surprises. The 3-pole design handles three-phase motor loads, and the integrated auxiliary switches (2 HQ contacts) give you a spare NO/NC pair for PLC feedback or alarm annunciation without adding a side-mount block.