Line-side protection for high-fault panels
The Siemens 3VA1225-6GF42-0AA0 is a SENTRON molded case circuit breaker sized for 250 A continuous, 4-pole, with a TM240 thermal-magnetic release tuned for line protection. The 220 kA breaking capacity at 240 V is the headline number — that is the interrupt rating at the lowest common distribution voltage, meaning it can ride through a bolted fault on a 240 V bus without self-destructing. At 415 V it still breaks 154 kA, and at 690 V it holds 17 kA, so the part covers both low-voltage and 690 V industrial feeds in the same frame.
Thermal derating — continuous current vs ambient
The 250 A rating holds flat up to 50 °C ambient. Above that it steps down: 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, 223 A at 70 °C. That is the curve a panel builder needs for enclosure sizing — if the panel ambient runs 60 °C, you lose 13 A from the nameplate. The power loss at full load is 57 W, which is the heat the breaker dumps into the enclosure; account for it in the thermal calculation.
Physical fit and panel integration
Footprint: 140 mm wide, 158 mm tall, 70 mm deep. That is a standard 4-pole MCCB form factor — mounts on a DIN rail or direct plate via the rear slots. IP40 on the front face means it is protected against tools and wires >1 mm but not sealed against water; keep it inside a rated enclosure. Rated insulation voltage is 800 V, so the internal creepage distances are sized for 690 V systems with margin.