What it is and what it does
The Siemens SENTRON 3VA1112-4EF32-0JA0 is a 3-pole molded case circuit breaker (MCCB) rated 125 A at 40 °C, designed for line protection in distribution panels. It carries a TM240 thermal-magnetic overcurrent release and an integrated shunt trip (STL) auxiliary release for remote tripping. The 121 kA breaking capacity at 240 V AC gives it headroom for high-fault installations — think service entrances or industrial feeder circuits where the available fault current is substantial.
Breaking capacity across voltage levels
Breaking capacity drops as system voltage rises: 121 kA at 240 V, 75.6 kA at 415 V, 52.5 kA at 440 V, and 11.9 kA at both 500 V and 690 V. That 11.9 kA at 690 V is the limiting case — if your panel feeds a 690 V motor drive, verify the fault current at that point doesn't exceed that figure, or you'll need a current-limiting upstream device.
Thermal derating and operating range
Rated current holds flat 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 the breaker lives in a hot enclosure — say, next to a transformer or in a sun-exposed panel — that 114 A at 70 °C is your real continuous limit, not the nameplate 125 A. Operating ambient range is -25 °C to 70 °C; storage range is -40 °C to 80 °C.
Mounting and panel fit
Dimensions are 130 mm height, 76.2 mm width, 70 mm depth — a standard SENTRON 3VA frame size that fits DIN-rail or panel-mount enclosures. The 3-pole width of 76.2 mm (3 inches) matches the common 25 mm-per-pole spacing. Rated insulation voltage is 800 V, so it's fine for 480/277 V and 600 V systems with margin.