What this MCCB delivers for the line
The Siemens 3VA1225-5GF42-0KA0 is a SENTRON molded case circuit breaker rated at 250 A continuous, 4-pole, with a TM240 thermal-magnetic overcurrent release. It's designed for line protection — meaning it sits at the incoming feeder or a high-current branch, not downstream on a motor or lighting panel. The 187 kA breaking capacity at 240 V tells you this breaker can clear a massive fault without welding contacts or venting gas back into the enclosure; at 415 V that figure drops to 121 kA, and at 690 V to 17 kA — still well above typical distribution transformer fault levels. The shunt trip (STL) auxiliary release lets a remote signal (E-stop, fire alarm, PLC output) trip the breaker independently of the overcurrent mechanism, which is useful for emergency-off circuits or load-shedding schemes.
Thermal derating — where the 250 A holds and where it doesn't
The 250 A rating is valid from 40 °C up to 50 °C ambient inside the panel. At 55 °C it derates to 243 A, at 60 °C to 237 A, at 65 °C to 230 A, and at 70 °C to 223 A. If your panel ambient runs above 50 °C — say a sealed enclosure near a furnace or in a hot climate — you need to account for the drop. The insulation voltage is rated at 800 V, so the breaker can sit on a 690 V system without derating the dielectric.