What it is and what it does
The Siemens SENTRON 3VA1112-4EF36-0AG0 is a 3-pole molded case circuit breaker (MCCB) rated for line protection, carrying a continuous current Iu of 125 A and a TM240 thermal-magnetic release. It's built for panel mounting — the 76.2 mm width and 70 mm depth fit standard distribution board cutouts, wiring up clean on a DIN rail or direct-mount plate. Breaking capacity is the headline here: 121 kA at 240 V AC, 75.6 kA at 415 V, and still 52.5 kA at 440 V. That puts it in the high-interrupting class for industrial feeders where fault current runs hot. At 690 V it still holds 11.9 kA, covering most 480V/600V panel applications without cascading upstream.
Thermal derating and real-world fit
The 125 A rating holds flat from 40 °C to 50 °C ambient — no derating needed in a typical ventilated enclosure. Above that it steps down: 120 A at 55 °C, 117.5 A at 60 °C, 115 A at 65 °C, and 112.5 A at 70 °C. If you're packing this into a tight, hot cabinet with other heat sources, the 70 °C curve is the one to spec against. TM240 release adjustable; tr max. 1 second. Auxiliary contact version includes 1 auxiliary switch plus 1 trip alarm switch HP.