The Siemens 5SN6640-7CN is a SENTRON miniature circuit breaker rated 40 A with a C-curve trip characteristic, 3P+N four-pole design, and a 6 kA breaking capacity at 400 V AC per EN 60898.
The 4-module width (72 mm) matches the standard 4-pole MCB slot — no surprises swapping into a panel laid out for SENTRON or comparable DIN-rail breakers. Solid conductors up to 25 mm² fit the terminals, which covers most 40 A feed circuits. Power loss is 3.3 W per pole in hot operating state at rated current — about 13.2 W total for all four poles. That's moderate for a 40 A breaker; check your enclosure's thermal derating if packing several breakers side by side.
Halogen-free and silicon-free construction, sealable for tamper-proofing. Supplementary devices can be installed (auxiliary contacts, shunt trips, alarm switches) via the accessory slots. Frequency rating is 50/60 Hz; maximum operating voltage is 440 V AC multi-phase.