What it is and what it does
The Siemens SENTRON 3VA1225-5EF32-0BC0 is a 3-pole molded case circuit breaker (MCCB) designed for line protection. It's rated at 250 A at 40 °C and delivers a 121 kA interrupting capacity at 415 V AC — that's enough to clear a serious fault on a distribution bus without the arc flashing upstream. The 800 V rated insulation voltage tells you it's built for 400 V class systems with margin. This breaker carries a factory-fitted undervoltage release (UVR) and two HQ auxiliary switches, so it's ready to drop into a safety circuit or a remote-trip scheme straight out of the box. The supplied basic switch variant is 3VA12255EF320AA0.
Breaking capacity — what the numbers mean
The interrupting ratings climb as voltage drops: 187 kA at 240 V, 121 kA at 415 V, 75.6 kA at 440 V, 30 kA at 500 V, and 17 kA at 690 V. For a 400 V class panel, the 121 kA figure at 415 V is the one that governs the SCCR sticker. If your transformer can push that much fault current, this breaker can stop it.
Thermal derating and real-world current
The 250 A rating holds steady up to 50 °C. Above that it derates: 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, and 223 A at 70 °C. If the breaker lives in a hot enclosure — say next to a drive or a transformer — that 223 A at 70 °C is the number to size against, not the nameplate 250 A.
Panel fit and integration
Footprint is 105 mm wide, 158 mm tall, 70 mm deep. That's a standard SENTRON 3VA frame size. Mounts on a DIN rail or direct to a backplate. Power loss is 59.5 W max — account for that heat in the enclosure calc, especially if you're stacking breakers.