What it is and what it does
The Siemens 3VA1112-3EF32-0AE0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection in distribution panels. It carries 125 A continuously at 40 °C ambient, with a 3-pole construction and a TM240 thermal-magnetic trip unit — meaning it handles overload and short-circuit protection in a single device, no separate relay needed. Rated insulation voltage is 800 V, so it's comfortable on 400 V and 480 V systems with headroom. Breaking capacity runs 75.6 kA at 240 V, 52.5 kA at 415 V, and 11.9 kA at 690 V — that's the fault current it can safely interrupt without welding contacts or venting plasma into the panel.
Thermal derating and panel fit
Full 125 A rating holds through 50 °C ambient. Above that it derates linearly: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, 114 A at 70 °C. If your panel internal temp runs hot — say a packed enclosure next to a furnace line — the 70 °C figure is the one to size against. Dimensions are 70 mm deep, 76.2 mm wide, 130 mm tall. That's a standard 3-pole MCCB footprint — fits most DIN-rail or direct-mount panel layouts. No undervoltage release, no ground-fault monitoring, no communication module on this variant; it's a straight line-protection breaker.