What it is and what it does
The Siemens SENTRON 3VA1040-3ED42-0AA0 is a 4-pole molded case circuit breaker (MCCB) rated for 40 A at 40 °C, designed for line protection in distribution panels. It carries a TM210 thermal-magnetic overcurrent release — meaning the thermal element handles overloads and the magnetic element handles short-circuits, with a fixed trip threshold. The rated insulation voltage is 800 V, so it's comfortable in 400 VAC and 480 VAC systems with headroom. Breaking capacity is the spec that decides whether this breaker clears a fault or welds shut. At 240 V it interrupts 75.6 kA; at 415 V it's 52.5 kA; at 440 V it drops to 32 kA; at 500 V and 690 V it holds at 7.5 kA. For a 40 A frame, those numbers are strong — it handles high available fault current on the secondary side of a typical 1000 kVA transformer without needing a current-limiting fuse upstream. Power loss is 10.8 W maximum — negligible for thermal budgeting in a crowded panel, but worth noting if you're packing multiple breakers side-by-side without forced ventilation.
Where it goes and how it fits
This MCCB mounts on a DIN rail or directly to a backplate via the standard 3VA footprint. The width is 101.6 mm (4 in), depth 70 mm (2.76 in), height 130 mm (5.12 in). That 70 mm depth is shallow enough to clear most gland plates and backpanel wiring ducts without interference — a common pain point with deeper frames. IP40 on the front means it's protected against tools and wires >1 mm, but not against dust ingress; keep it inside a closed enclosure. Operating temperature range is -25 °C to 70 °C, with the full 40 A rating holding up to 50 °C. Above that it derates linearly to 37 A at 70 °C. Storage range is -40 °C to 80 °C. If the panel sits in a hot attic or near a furnace, check the derating curve against your actual load.