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.
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. 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.
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. Locking slide integrated into the housing accepts a padlock, wire seal, or cable tie for lockout/tagout.