What the ratings mean for fit
The Siemens 3VA1112-4FF42-0AA0 is a SENTRON molded case circuit breaker — 4-pole, line-protection version, with a TM240 thermal-magnetic release. Rated continuous current Iu is 125 A, and it holds that rating flat from 40 °C through 50 °C (–), then derates to 114 A at 70 °C. That thermal curve matters if this breaker lives in a warm enclosure: at 55 °C you still get 122 A, so for a 125 A bus feeding a motor control center, you have headroom in a typical 40 °C panel. Interrupting capacity is the other headline: 121 kA at 240 V, 76 kA at 415 V, 53 kA at 440 V, and 11.9 kA at both 500 V and 690 V (–). That 121 kA at 240 V is a high-fault rating — typical for a service entrance or a large distribution panel where the transformer impedance is low. The 11.9 kA at 690 V is the ceiling for industrial 690 V drives; if your SCCR study calls for more than that at 690 V, this breaker won't coordinate. Rated insulation voltage Ui is 800 V, and the DC rating maxes at 600 V. The N-conductor protection is set at 50% — that's the factory default for the 4-pole version, meaning the neutral pole trips at half the phase current. If you need 100% neutral protection, that's a different order code.
Panel integration and approvals
Mounts on a DIN rail or panel-mount baseplate — the 101.6 mm width and 70 mm depth fit the standard SENTRON 3VA footprint. IP40 on the front means it's protected against tools and wires >1 mm, but not against water ingress; keep it inside a rated enclosure. The 130 mm height clears most 200 mm tall distribution boards. Power loss is 28.1 W max at full rated current — that's the heat you need to vent in a sealed cabinet. Operating temperature range is -40 °C to 70 °C (–), storage from -40 °C to 80 °C (–). The 20,000-cycle endurance is mechanical; electrical endurance will be lower depending on the fault current cleared.