What it is and what the ratings mean
The Siemens 3VA1112-5EF32-0KH0 is a SENTRON molded case circuit breaker (MCCB) designed for line protection — meaning it sits at the incoming feeder or main distribution point, not downstream on a motor circuit. Rated 125 A continuous at 40 °C, it holds that current all the way up to 50 °C before it starts a gentle derating curve: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, 114 A at 70 °C. That thermal profile matters if you're packing this into a high-ambient panel — the 125 A frame doesn't lose much until you push past 50 °C. The interrupting ratings are the headline: 187 kA at 240 V, 121 kA at 415 V, 75.6 kA at 440 V, and 17 kA at both 500 V and 690 V. That 187 kA figure at 240 V tells you this breaker can clear a fault on a high-capacity transformer secondary without the arc re-striking — it's sized for large industrial service entrances, not branch panels. The 121 kA at 415 V covers the common European three-phase distribution voltage, and the drop to 17 kA at 690 V is still respectable for a 125 A frame in a 690 V system.
Integration and panel fit
Three-pole, 76.2 mm wide (3 inches), 130 mm tall, 70 mm deep — that's a standard SENTRON 3VA footprint. It mounts on a DIN rail or panel-mount plate, and the 70 mm depth leaves room behind a 200 mm deep enclosure for wiring and the shunt trip wiring. The shunt trip (STL) release is built in, so you can remotely trip the breaker from an emergency-stop circuit or a PLC output without adding an external undervoltage module. Two auxiliary switches plus one trip alarm switch (HQ) are also integrated — enough for status feedback to a PLC or SCADA system.