What this MCCB carries — and what that means on the rail
The Siemens SENTRON 3VA1112-4EF36-0HC0 is a 3-pole molded case circuit breaker rated 125 A at 40 °C, sized for line-protection duty in distribution panels. Its interrupting capacity hits 121 kA at 240 V AC and 75.6 kA at 415 V AC — that's the fault-clearing muscle you need when the available short-circuit current is high and you want selectivity upstream without blowing the main. Rated insulation voltage is 800 V, so it's comfortable on 690 V systems. Power loss runs 28.1 W max — factor that into enclosure thermal calcs if you're packing several breakers side by side. It ships with a shunt trip (STL) release for remote tripping and two HQ auxiliary switches for status feedback to a PLC or annunciator panel. The basic switch assembly carries order code 3VA11124EF360AA0.
Mounting and fit — DIN-rail footprint, no surprises
Width is 76.2 mm (3 in), depth 70 mm (2.76 in), height 130 mm (5.12 in). That's the standard 3-pole MCCB footprint for the SENTRON 3VA platform — it clips onto the DIN rail and lines up with the busbar system. If you're swapping into an existing panel, measure the mounting depth: 70 mm leaves room for rear-connected busbars without crowding the backplane.
Thermal derating — what the 125 A rating actually delivers
The breaker holds its full 125 A rating from 40 °C through 50 °C. Above that it starts to taper: 122 A at 55 °C, 120 A at 60 °C, 117 A at 65 °C, and 114 A at 70 °C. If your panel ambient runs hot, you're still getting 114 A at the top of the operating range — no derating cliff, just a gentle slope. Operating temperature range is -25 °C to 70 °C; storage range is -40 °C to 80 °C. That covers most indoor industrial environments and unheated warehouses.