The Siemens SENTRON 3VA1225-4EF32-0KC0 is a 3-pole molded case circuit breaker rated 250 A continuous at 40 °C through 50 °C, with a 121 kA interrupting capacity at 240 V and 75.6 kA at 415 V. That interrupting curve — 52.5 kA at 440 V, 17 kA at 500 V, 11.9 kA at 690 V — tells you this breaker is sized for high-fault industrial service where the available short-circuit current is substantial, not for a light commercial panel. It's a line-protection design, meaning the trip unit is calibrated for feeder and main applications rather than motor or generator protection.
Thermal derating and auxiliary fit
The 250 A rating holds flat from 40 °C to 50 °C, then steps down: 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, 223 A at 70 °C. Max power loss is 57 W; account for that heat in a sealed enclosure.
Dimensions: 105 mm wide, 158 mm tall, 70 mm deep. The 70 mm depth leaves room behind a 200 mm deep enclosure for wiring and the shunt trip leads.