What the ratings mean for fit
The Siemens SENTRON 3VM1112-3EE32-0AA0 is a 3-pole molded case circuit breaker (MCCB) designed for line protection, rated 125 A at 40 °C. That 125 A is the continuous current it carries without tripping at 40 °C ambient — the rating you size your feeder for. Above that temperature, it derates: still 125 A at 50 °C, then 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C. If your panel runs hot, the actual ampacity is lower than the nameplate; plan the load accordingly. Breaking capacity is the fault current it can safely interrupt. At 240 V it handles 76 kA; at 415 V, 53 kA; at 440 V, 32 kA; at 500 V, 12 kA. The 76 kA at 240 V means it clears high-fault conditions on a 240 V secondary without upstream coordination issues — useful for large transformer-fed panels. The 415 V figure (53 kA) is the one most relevant for 400 V industrial distribution in Europe and Asia. The overcurrent release is a TM220 thermal-magnetic type, so it provides both thermal (overload) and magnetic (short-circuit) protection in one unit. Insulation voltage is rated 800 V, meaning the internal clearances and creepage distances are designed for 800 V systems — it can be used on 690 V line-to-line supplies where available. The front face carries IP40 protection, so it's protected against tools and small objects but not sealed against moisture; mount it inside a panel or enclosure.
Panel fit and mounting
Dimensions: 130 mm height, 76.2 mm width, 70 mm depth. The 76.2 mm width (3 inches) is standard for a 3-pole MCCB in this frame size — it fits the typical DIN-rail or panel-mount cutout without surprises. Maximum power loss is 23 W, so plan for that heat dissipation inside the enclosure; if you pack multiple breakers side by side, the internal temperature rise may push you into the derated current column above 55 °C. No undervoltage release, no shunt trip (voltage trigger), no ground-fault monitoring, no communication function — this is a plain thermal-magnetic breaker for straightforward line protection. If you need remote tripping or ground-fault sensing, you'd step up to a 3VA-series or add external accessories. The trip indicator is not present, so visual trip status is read from the handle position only.