What this MCCB is and what it does
The Siemens 3VA1225-4GF42-0AJ0 is a SENTRON molded case circuit breaker (MCCB) rated for 250 A continuous, with a TM240 thermal-magnetic overcurrent release. The 4-pole design covers three-phase plus neutral, and the line-protection variant is set up for feeder or main breaker duty in distribution panels. The interrupting capacity varies by system voltage: 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 — so the available fault current at the installation point determines which voltage column governs the selection.
Thermal derating and panel integration
The breaker carries its full 250 A rating up to 50 °C ambient; above that it derates linearly to 223 A at 70 °C. In a sealed or high-ambient enclosure, the 57 W maximum power loss needs to be factored into the thermal budget — especially when grouping multiple breakers. The 158 mm height, 140 mm width, and 70 mm depth fit standard Siemens SENTRON mounting footprints, and the trip indicator gives a quick visual on the panel door.