What this MCCB carries and where it fits
The Siemens 3VA1112-5FD46-0AA0 is a SENTRON molded case circuit breaker rated 125 A continuous at 40 °C, with a TM210 thermal-magnetic trip unit. Four poles cover three-phase plus neutral or a four-wire distribution circuit. The 187 kA breaking capacity at 240 V AC handles high-fault service-entrance or sub-distribution boards; at 415 V it still interrupts 121 kA, and at 690 V it holds 17 kA. That spread tells you this breaker is sized for industrial line-ups where available fault current varies by voltage level — not a residential main.
Thermal derating — the real ampacity in a warm panel
The 125 A rating holds flat from 40 °C through 50 °C. Above that it steps down: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, 114 A at 70 °C. If your enclosure runs hot — say a packed MCC bucket — size the load to the derated number, not the nameplate. The TM210 trip unit is fixed thermal plus magnetic; no adjustment dial, so the curve is what it is.
Panel fit and wiring
The case measures 130 mm tall, 101.6 mm wide, 70 mm deep — a 4-inch wide footprint that matches the 3VA1110/1112 family. It mounts on a DIN rail or bolts directly to a backplate. Front IP40 keeps dust out of the enclosure but it's not washdown-rated; keep it behind a gland plate or cabinet door. Power loss at full load is 28.1 W — factor that into your thermal budget if you're stacking breakers in a small enclosure.