What this 250 A MCCB does on the line
The Siemens SENTRON 3VA1225-4GF42-0DA0 is a 4-pole molded case circuit breaker rated at a fixed 250 A, designed for line protection in distribution panels. It carries a TM240 thermal-magnetic overcurrent release — the thermal element handles overloads, the magnetic element clears short-circuits. Breaking capacity is 121 kA at 240 V, dropping to 75.6 kA at 415 V and 52.5 kA at 440 V, so it can interrupt high fault currents on the secondary side of a step-down transformer or at a main distribution board. The 800 V rated insulation voltage gives headroom for 690 V systems. An undervoltage release (UVR) is built in — if the supply voltage drops below the release threshold, the breaker trips. That's useful for motor circuits where you want the breaker to drop out on a brownout rather than let the motor stall and draw locked-rotor current. The UVR is factory-fitted; no separate module to wire in.
Thermal derating and panel fit
At 40 °C the breaker carries its full 250 A. It holds 250 A up to 50 °C, then derates to 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, and 223 A at 70 °C. If the panel ambient runs hot — say a packed enclosure near a furnace line — you need to account for that drop. The 59.5 W maximum power loss also adds heat inside the enclosure; factor it into the thermal budget. Dimensions are 140 mm wide, 158 mm high, 70 mm deep. That's a standard SENTRON 3VA frame size for 250 A — it fits the same DIN-rail or mounting-plate footprint as other 3VA breakers in this current class. The 4-pole width is wider than a 3-pole unit; check the enclosure gland plate and busbar spacing before committing.