What this MCCB is and what it does
The Siemens SENTRON 3VA1112-3ED12-0AA0 is a 1-pole molded case circuit breaker (MCCB) rated 125 A at 40 °C, built for line protection in commercial and industrial distribution panels. It uses a TM210 thermal-magnetic overcurrent release — the thermal element handles overloads, the magnetic element catches short circuits — and carries a 52.5 kA interrupting rating at 240 V AC, which drops to 7.5 kA at 415 V AC. The 70 mm depth and 25.4 mm width mean it fits standard panelboard slots without crowding adjacent poles.
Thermal derating — what the 125 A rating actually means
The 125 A rating holds flat from 40 °C to 50 °C, then begins a gradual decline: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C. That derating curve is the one you size against — if your panel ambient runs 60 °C, this breaker is good for 120 A continuous, not 125 A. Ignoring the curve is how you nuisance-trip a line.