What this MCCB is and where it lands
The Siemens 3VA1225-4GF42-0AD0 is a SENTRON molded case circuit breaker (MCCB) for line protection. It is a 4-pole, 250 A fixed-rated unit with a TM240 thermal-magnetic release. Rated insulation voltage is 800 V. Interrupting capacity is voltage-dependent: 121 kA at 240 V, 75.6 kA at 415 V, 52.5 kA at 440 V, 17 kA at 500 V, and 11.9 kA at 690 V. That's the fault current it can safely clear without welding contacts or venting gas into the panel — match the available fault current at your service entrance to these numbers. Thermal derating is published from 40 °C up: full 250 A through 50 °C, then 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, and 223 A at 70 °C. If your panel ambient runs hot, size up or accept the reduced continuous current.
Panel fit and auxiliary complement
Footprint is 140 mm wide, 158 mm high, 70 mm deep. That's a standard SENTRON 3VA form factor — fits the same DIN-rail or screw-mount pattern as other 3VA breakers in this frame. Depth of 70 mm means it clears most shallow enclosures without a gland-plate conflict. Ships with three HQ auxiliary switches built in. No undervoltage release, no ground-fault monitoring, no communication module. The basic switch assembly is order code 3VA12254GF420AA0 — useful if you're ordering a spare mechanism separately.