The 5SY6402-8 is a 4-pole miniature circuit breaker from the Siemens SENTRON 5SY6 series, rated 2 A at 400 V AC with a D tripping characteristic. Mounting is snap-on for 35 mm DIN rail (quick assembly system), any position. Terminal capacity accepts 0.75–35 mm² solid or stranded, so it handles both control-circuit tails and power feeders.
Approvals include EN 60898, IEC 60947-2, UL 1077, and CSA C22.2 No.235 — the UL/CSA ratings are lower (5 kA at AC) but sufficient for North American branch-circuit protection where the available fault current is known to be under that threshold. The part carries touch protection and is sealable, which matters for panel builders who need to lock settings after commissioning.