What it is and what it does
The Siemens 3VA1112-4EF32-0DC0 is a 3-pole SENTRON molded case circuit breaker (MCCB) rated 125 A at 40 °C, designed for line protection in distribution panels. Its interrupting capacity hits 121 kA at 240 V AC and 75.6 kA at 415 V AC — numbers that matter when you're coordinating selectivity downstream of a transformer or a large motor starter. The breaker carries an 800 V rated insulation voltage and includes an undervoltage release (UVR) plus two HQ auxiliary switches as standard. Max power loss is 30.6 W, so factor that into enclosure thermal calculations.
Ratings and what they mean for your panel
Rated current holds at 125 A from 40 °C through 50 °C, then derates to 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C. If your panel ambient runs above 50 °C, you lose 3–11 A — enough to trip a borderline feeder on a hot day. The interrupting curve is steep: 75.6 kA at 415 V drops to 52.5 kA at 440 V and 11.9 kA at 500 V or 690 V. At higher voltages, the breaker still clears faults, but the available fault current must stay under the lower rating.
Physical fit and integration
Dimensions: 130 mm high, 76.2 mm wide, 70 mm deep. Mounts on a DIN rail or directly to a panel backplate. The 3-pole footprint matches the standard SENTRON 3VA frame, so it swaps into existing cutouts without re-drilling.