Breaking capacity across voltage levels — the real fault-clearing envelope
The Siemens 3VA1225-4GF42-0AB0 is a 4-pole SENTRON molded case circuit breaker rated for 250 A continuous current (Iu) with a TM240 thermal-magnetic overcurrent release. Its breaking capacity is voltage-dependent: 121 kA at 240 V, 75.6 kA at 415 V, 25 kA at 440 V, and 11.9 kA at 690 V. That 121 kA figure at 240 V covers high-fault utility feeds or transformer secondaries where available fault current exceeds typical distribution gear; the 11.9 kA at 690 V still clears motor-drive bus faults in most industrial installations. The 800 V rated insulation voltage (Ui) confirms the internal clearances support 690 V line-to-line switching without tracking.
Thermal derating — where the real ampacity lands
The 250 A rating holds flat from 40 °C through 50 °C. Above that, the TM240 release derates: 243.3 A at 55 °C, 236.5 A at 60 °C, 229 A at 65 °C, and 223 A at 70 °C. For a panel that runs at 55 °C ambient — common in sealed enclosures with solar or drive heat — the usable continuous current drops to 243 A. The operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C.
Panel fit and auxiliary wiring
Dimensions are 158 mm high, 140 mm wide, 70 mm deep. The 140 mm width is standard for a 4-pole MCCB in this frame class — verify the gland plate or DIN-rail cutout matches before committing the BOM. The breaker ships with 2 auxiliary switches HP (high-performance) built in, which provide independent status feedback for PLC or safety relay monitoring. No undervoltage release, no shunt trip, no communication module on this variant — it is a straight line-protection breaker with the TM240 release. IP40 on the front face means it is protected against tools and wires >1 mm; the enclosure must handle side and rear ingress.