The Siemens 5SP3240-3 is a SENTRON main miniature circuit breaker — 2-pole, E tripping characteristic, rated 40 A at 400 V AC, 50 Hz. The E curve means it's built for selective coordination with upstream devices in residential and infrastructure panels, with a delayed trip that lets downstream MCBs clear a fault first. A 25 kA breaking capacity per EN 60898 matches the fault level at the service entrance in most European domestic and light commercial builds.
What the ratings mean on the panel
40 A at 30 °C ambient, derated to 38 A at 40 °C and 35 A at 55 °C — so if this breaker lives in a hot enclosure or next to other heat-generating devices, factor that 5 A drop into your load calculation. The 25 kA rated short-circuit capacity at 400 V (per EN 60898) tells you it can safely interrupt a fault up to that level without welding its contacts or failing catastrophically — that's the SCCR you need for the service entrance. Insulation voltage rated 690 V gives headroom above the 400 V operating level. It's a 2-pole breaker (2P design), so it switches both phase and neutral — common for single-phase final subcircuits in European residential and infrastructure panels where the neutral needs disconnection. Three modular width units wide on a 35 mm DIN rail per EN 60715, so it takes up 52.5 mm of rail space.
Mounting and integration
Snaps onto 35 mm DIN rail (EN 60715). Terminal capacity goes from 2.5 mm² up to 50 mm² solid or stranded — that's a wide clamping range for feeding through larger incoming cables. Saddle terminals are fitted, which grip the conductor firmly without damaging strands. The enclosure is IP40 with conductors connected, so it's fine inside a clean indoor panel but not for wet or dusty environments. Locking slide integrated into the housing accepts a padlock, wire seal, or cable tie for lockout/tagout.