What this MCCB is and what it does
The Siemens 3VA1225-4EF32-0KB0 is a SENTRON molded case circuit breaker (MCCB) built for line protection — the main disconnect and fault interrupter between your transformer and the distribution bus. Three poles, rated 250 A continuous at 40 °C, with a shunt trip release (STL) already fitted for remote or undervoltage-triggered opening. It's the kind of breaker you spec into a panel when you need one device to handle both the load current and a hard fault without welding its contacts shut.
Interrupting capacity — what those voltage columns mean
The interrupting ratings tell you how much fault current this breaker can safely clear at different system voltages. At 240 V it's rated for 121 kA — enough for a high-capacity transformer secondary. At 415 V it handles 75.6 kA, at 440 V it's 52.5 kA, at 500 V it drops to 17 kA, and at 690 V it's 11.9 kA. The 690 V figure is the one to watch on a 600 V class system: 11.9 kA is adequate for most industrial service-entrance applications but not for a high-fault utility feed. Match the voltage you actually run, not the highest number on the nameplate.
Thermal derating — the current it carries when the panel gets hot
This breaker is rated 250 A continuous from 40 °C up to 50 °C. Above that it starts to derate: 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, and 223 A at 70 °C. If your panel sits near a hot motor drive or a steam line, the 70 °C figure is the one that governs your load — you lose about 11% of the headroom. The rated insulation voltage is 800 V, so the internal clearances hold up at the higher temperature.
Shunt trip release — what it adds to the breaker
The 3VA1225-4EF32-0KB0 ships with a shunt trip (STL) auxiliary release. That means you can trip the breaker remotely by applying a control voltage to the shunt trip coil — useful for emergency-stop circuits, undervoltage protection, or a PLC-driven shutdown. The breaker also carries two auxiliary switches (HP type) for status feedback to the control system. No undervoltage release is fitted from the factory, so if you need UVR you'll add it in the field or order a different variant.
Physical fit — panel and enclosure dimensions
Width 105 mm, height 158 mm, depth 70 mm. Maximum power loss is 57 W.