What this MCCB is and where it fits
The Siemens SENTRON 3VM1112-4GD42-0AA0 is a 4-pole molded case circuit breaker rated 125 A continuous at 40 °C, with a TM210 thermal-magnetic trip unit providing LI protection (long-time and instantaneous). It is designed for line protection in distribution panels and switchboards, sized to fit a standard 101.6 mm wide (4-inch) footprint at 70 mm depth — a common form factor for panel builders working with 4-pole MCCBs in IEC-style enclosures. Breaking capacity runs 121 kA at 240 V AC, 76 kA at 415 V AC, 53 kA at 440 V AC, and 12 kA at 500 V AC — these numbers govern selectivity coordination with downstream breakers. The rated insulation voltage (Ui) is 690 V, so it is comfortable in 400 V and 480 V systems with headroom.
Thermal derating and trip unit
The TM210 trip holds 125 A flat 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. The adjustable instantaneous pickup (li) maxes at 1,250 A — roughly 10x the 125 A frame, which is a typical setting for motor branch circuits or high-inrush loads. Power loss at rated current is 23 W maximum, relevant for thermal management inside a sealed panel. Front-face protection is IP40 — splash protection is not built in; the breaker belongs behind a panel door or in a dead-front switchboard. Operating temperature range is -25 °C to 70 °C, storage from -40 °C to 80 °C.