125 A MCCB with 75.6 kA interrupting — selectivity headroom for distribution panels
The Siemens SENTRON 3VA1112-3EF32-0AD0 is a 3-pole molded case circuit breaker (MCCB) rated for 125 A continuous current at 40 °C ambient, with a TM240 thermal-magnetic trip unit that provides adjustable time-delay response up to 1 second at 6× Iu. Its interrupting capacity hits 75.6 kA at 240 V and 52.5 kA at 415 V, which gives selectivity headroom downstream of a larger main breaker in 400 V distribution — you can clear a bolted fault without cascading the whole panel. The 800 V rated insulation voltage (Ui) means it's comfortable in 480 V or 600 V industrial feeds where phase-to-phase stress is higher than line-to-neutral. This is a line-protection version (no voltage trigger, no undervoltage release, no ground-fault monitoring) — it's built for straightforward overcurrent and short-circuit protection on feeders or large motor branch circuits, not for GFP or shunt-trip applications. The three auxiliary switches (HQ type) give you status feedback for PLC or SCADA; no communication module onboard.
Thermal derating and panel fit — what the 125 A rating really means
The 125 A rated continuous current (Iu) holds flat from 40 °C to 50 °C, then derates to 120 A at 55 °C, 117.5 A at 60 °C, 115 A at 65 °C, and 112.5 A at 70 °C. If the breaker lives in a sealed, uncooled enclosure near transformers or drives, use the 55 °C column for your load calculation. The IP40 front protection means it's fine in a clean panel but not washdown-rated — keep it behind a gland plate. Physical dimensions: 130 mm height, 76.2 mm width (3-module wide on DIN), 70 mm depth. The 70 mm depth is shallow enough for most 200 mm deep enclosures; verify clearance for the auxiliary switch wiring exit on the front face.