The Siemens 5SP3740 is a 1-pole SENTRON selective miniature circuit breaker (MCB) rated 40 A at 230 V AC, 50 Hz, with an E tripping characteristic and a 25 kA breaking capacity per EN 60898. That 25 kA rating means it can safely interrupt a fault current up to 25 000 A without welding its contacts or cascading damage upstream — a key spec for high-fault-capacity service-entrance or sub-distribution panels where standard 6 kA or 10 kA MCBs would fail.
Mounts on standard 35 mm DIN rail (standard rail) and occupies 2 width units (36 mm). The enclosure depth is 92 mm. Terminals accept 2.5 mm² minimum up to 50 mm² solid or stranded copper — that 50 mm² maximum is unusual for a 1-pole MCB and allows feeding through heavy-gauge incoming supply conductors without a separate terminal block. Saddle terminals are fitted. IP20 with connected conductors; overvoltage category IV, surge voltage resistance 6 kV. Switch position indicator shows green for OFF, red for ON. Sealable.