What the 125 A rating means for your panel
The Siemens SENTRON 3VA1112-3EF36-0AE0 is a 3-pole molded case circuit breaker rated 125 A continuously at 40 °C, 45 °C, and 50 °C without derating — meaning the full 125 A is available in a typical 40 °C panel environment. Above 55 °C the current tapers: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C. If your enclosure runs hot, the 70 °C figure (114 A) is the one to size against. Breaking capacity reaches 75.6 kA at 240 V, 52.5 kA at 415 V, 32 kA at 440 V, and 11.9 kA at both 500 V and 690 V. For a 480 V distribution panel the 32 kA at 440 V is the closest published figure — verify your available fault current against that level. Rated insulation voltage is 800 V, and the breaker is designed for line protection (not motor or generator protection). It carries no undervoltage release, no ground-fault monitoring, and no communication function — this is a straightforward thermal-magnetic (TM240) overcurrent release for feeder or branch-circuit duty.
DIN-rail footprint and panel fit
At 70 mm deep, 76.2 mm wide, and 130 mm tall, this MCCB fits standard 3-pole SENTRON panel cutouts and busbar systems. The 76.2 mm width (3 in) matches the common 3-pole MCCB footprint for 125 A class — no adapter plate needed for most Siemens switchboards or distribution boards. Maximum power loss is 28.1 W at rated load — factor that into your enclosure thermal budget, especially if multiple breakers are ganged in a sealed cabinet.