What the ratings mean for fit
The Siemens SENTRON 3VA1112-6GD42-0AA0 is a 4-pole molded case circuit breaker (MCCB) rated for line protection at 125 A continuous (Iu = 125 A). The interrupting capacity is the headline: 220 kA at 240 V AC, dropping to 154 kA at 415 V, 75.6 kA at 440 V, and 17 kA at both 500 V and 690 V. That 220 kA at 240 V means this breaker can safely clear a fault current of that magnitude without rupturing — critical for high-fault installations like transformer secondaries or large motor control centers where upstream fault current is high. The 125 A rating holds up to 50 °C ambient; above that it 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 runs hot near the top of that range, the 125 A frame still carries 114 A continuously — enough for most 100 A feeder circuits. The overcurrent release is a TM210 — thermal-magnetic, fixed at 10× Iu (1250 A instantaneous pickup). That's a standard motor or distribution curve; it coordinates well downstream of a larger MCCB or upstream of contactors. The 800 V rated insulation voltage (Ui) and 600 V DC max operational voltage (Ue) mean this breaker also works in DC circuits up to 600 V, though the interrupting capacity on DC isn't listed here — the manual covers that. The N-conductor protection is 100%, so the neutral pole is fully rated, not just switched. Front IP40 keeps dust out of the panel face; the rest of the breaker is inside the enclosure.
Panel integration
The breaker measures 70 mm deep, 101.6 mm wide, and 130 mm high. That 101.6 mm width (4 inches) is standard for a 4-pole MCCB in this frame size — it occupies four 25 mm pole spaces on a DIN rail or panel-mount footprint. The depth of 70 mm (2.76 in) is shallow enough for most 200 mm deep enclosures; verify gland plate clearance if mounting near the back wall. The front face is IP40, so the breaker is protected against solid objects larger than 1 mm, but not sealed against moisture — keep it inside a rated enclosure for washdown areas.