125 A MCCB with high interrupting capacity
The Siemens 3VA1225-5FF42-0DC0 is a SENTRON molded case circuit breaker rated for 125 A continuous current across all four poles, with a maximum interrupting capacity of 187 kA at 240 V AC. That 187 kA rating means it can safely clear a fault current up to that level without the arc flashing over or the case rupturing — critical for high-fault installations like large transformer secondaries or busway taps where available fault current is substantial. At 415 V it still interrupts 121 kA, and at 690 V it holds 17 kA, so the breaker's selectivity holds across common industrial voltage levels. The 4-pole design makes this unit suitable for three-phase plus neutral protection in TN or TT systems, or for dual-feed applications where all poles need coordinated interruption. The built-in undervoltage release trips the breaker when supply voltage drops below a threshold — a standard requirement for emergency-stop circuits and machine safety interlocks in European-style panels.
Thermal derating and panel integration
The breaker's 125 A rating holds up to 50 °C ambient (–). Above that, it derates linearly: 243 A at 55 °C, 237 A at 60 °C, 230 A at 65 °C, and 223 A at 70 °C (–). In a sealed enclosure or near other heat sources, factor that derating into the load calculation — the 70 °C operating maximum is the breaker's internal limit, not a recommendation to run at full current at that temperature. The 59.5 W maximum power loss needs ventilation in a tight cabinet; a 140 mm wide × 158 mm tall × 70 mm deep footprint fits standard MCCB cutouts but watch the depth for gland-plate clearance.