What this MCCB is and what it does
The Siemens 3VA1225-4EF42-0DH0 is a SENTRON molded case circuit breaker (MCCB) rated for line protection. It carries 250 A continuous current (Iu) across four poles, with a TM240 thermal-magnetic release that handles overloads and short circuits without external power. The 121 kA interrupting rating at 240 V drops to 75.6 kA at 415 V, 25 kA at 440 V, and 11.9 kA at 690 V — so the available fault current at your service voltage decides whether this breaker clears the fault or the arc flash gets ugly first.
Thermal performance and panel fit
This breaker holds its full 250 A rating up to 50 °C ambient; above that it derates in steps — 243.3 A at 55 °C, 236.5 A at 60 °C, 229 A at 65 °C, 223 A at 70 °C. If your panel runs hot near the top of the enclosure, account for that curve before sizing the downstream conductors. Dimensions are 158 mm high, 140 mm wide, 70 mm deep — standard MCCB footprint for a 4-pole frame this size, with IP40 protection on the front face.
Auxiliary contacts and undervoltage release
Factory-fitted with 2 auxiliary switches plus 1 trip alarm switch (HQ configuration) and an undervoltage release (UVR). The auxiliary contact version is 3VA9608-0BB25. That UVR means the breaker drops open if control voltage falls below the dropout threshold — useful for emergency-stop circuits or undervoltage protection on motor feeders where you don't want automatic reclose after a dip.