What it is and what it does
The Siemens 5SP3450-3 is a SENTRON main miniature circuit breaker, 4-pole, rated 50 A at 400 V AC. Its 25 kA breaking capacity per EN 60898 means it can safely interrupt a fault current up to that level without welding contacts or cascading upstream — sized for residential and infrastructure service entrances where the prospective short-circuit current is known to be that high. Characteristic E is the tripping curve here — it's a delayed thermal-magnetic release designed for circuits with moderate inrush, like groups of fluorescent lighting or small transformers. The magnetic trip threshold is higher than a B or C curve, so nuisance tripping on startup is less likely, but it still clears a hard fault within the rated breaking capacity.
Key ratings and what they mean for fit
The 50 A rating is at 30 °C ambient. At 40 °C it derates to 47.5 A, at 50 °C to 45 A. If your panel ambient runs above 30 °C, size the continuous load against the derated figure, not the 50 A nameplate. The 690 V rated insulation voltage (Ui) and 6 kV surge voltage resistance (overvoltage category IV) confirm it's built for the line side of a building main distribution board, not just sub-panel duty. Pollution degree 3 means it's rated for the conductive-dust and humidity conditions typical in an industrial or infrastructure enclosure — not a clean room, but not a sealed outdoor cabinet either. The IP40 rating (with connected conductors) is standard for a DIN-rail MCB inside a closed panel; it's not for washdown or outdoor exposure.
Mounting and integration
Snap-on standard rail (DIN rail) mounting. 6 modular width units (MW) wide — that's about 108 mm on the rail. The 128 mm height and 76.3 mm depth fit a standard distribution board depth; the depth figure is the body only, not including the handle throw or conductor bend radius. Terminals accept solid or stranded copper from 2.5 mm² up to 50 mm² — covers the range from a 6 mm² subfeed to the 35 mm² or 50 mm² main feeder. Saddle terminals and box-terminal infeed are both present; the locking device (integrated slide, lockable with a padlock, wire seal, or cable tie) is useful for utility-metering or safety-disconnect applications where unauthorized operation must be prevented. Sealable, per the evidence — the enclosure can be sealed to prevent tampering, which is often a requirement for revenue-metering or landlord sub-metering installations.
Sourcing and lifecycle
Shock resistance is rated at 30 g for at least 3 impacts of 11 ms duration — that's the mechanical robustness for transport and seismic events, not a continuous vibration spec. For applications with sustained vibration (near a large motor or compressor), you'd want additional dampening or a different mounting method.