What the ratings mean for fit
The Siemens 3VA1112-5EF32-0AB0 is a SENTRON molded case circuit breaker (MCCB) built for line protection in distribution panels. Its 125 A continuous rating at 40 °C holds flat through 50 °C — no derating needed until you cross 55 °C, where it drops to 122 A, and then 120 A at 60 °C. That thermal curve matters when the breaker sits in a warm enclosure alongside other heat sources; you can load it to 125 A without headroom padding up to 50 °C ambient. The interrupting capacity tells you where this breaker can live in the fault-current hierarchy: 187 kA at 240 V, 121 kA at 415 V, 75.6 kA at 440 V, and 17 kA at 500 V and 690 V. That 187 kA figure at 240 V is high enough for most service-entrance or main-tie applications on 240 V systems; at 415 V the 121 kA still covers heavy industrial feeds. The sharp drop to 17 kA above 500 V means you need to verify the available fault current at the point of installation if the system voltage exceeds 500 V. Three-pole construction with a TM240 thermal-magnetic release — the TM designation means fixed thermal and magnetic trip settings, not adjustable. No undervoltage release, no shunt trip, no ground-fault monitoring on this variant. The auxiliary switch bay carries two HP-style switches for status feedback to a PLC or indication lamp.
Panel fit and integration
Dimensions are 130 mm high, 76.2 mm wide, 70 mm deep — a standard MCCB footprint for 125 A frames. It mounts directly to a DIN rail or panel-mount adapter; the 70 mm depth leaves room for rear-connected busbars in a typical distribution cabinet. Rated insulation voltage is 800 V, so it can be used in 690 V systems with appropriate clearance. Power loss is 28.1 W maximum at rated load. That's moderate for a 125 A frame — account for it in enclosure thermal calculations if the panel is densely packed.