125 A MCCB with 75.6 kA interrupting rating — line protection for main feeder panels
The Siemens 3VA1112-3EF36-0CC0 is a 3-pole SENTRON molded case circuit breaker rated 125 A at 40 °C, with a breaking capacity of 75.6 kA at 240 V AC. The interrupting rating drops to 52.5 kA at 415 V, 32 kA at 440 V, and 11.9 kA at 500/690 V — so the available fault current at the panel location determines which voltage column governs the selection. This is a line-protection design (not feeder or motor-protection), meaning the thermal-magnetic trip curve is shaped for cable and busbar protection rather than motor inrush. An undervoltage release is fitted as standard, which trips the breaker if the control voltage drops below a set threshold — useful for safety circuits that need to fail safe on loss of control power.
Thermal derating and panel integration
Rated current holds flat at 125 A from 40 °C up to 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. In a sealed enclosure with multiple breakers ganged, the ambient temperature inside the panel can easily exceed 50 °C; the derating curve tells you the actual continuous current the breaker can carry without nuisance tripping. The unit occupies a 76.2 mm (3 in) width on the DIN rail, with a depth of 70 mm and height of 130 mm — fits standard panel layouts for 125 A class MCCBs. Maximum power loss is 30.6 W, which contributes to the enclosure heat budget.