Siemens 5SY6540-8 — 40 A D-Curve MCB for Industrial Branch Circuits
The Siemens 5SY6540-8 is a SENTRON 5SY6 miniature circuit breaker rated 40 A with a D tripping characteristic, in a 2-pole (1P+N) form factor. It snaps onto a DIN rail via the quick-assembly system and fits any mounting position — the 70 mm installation depth and 36 mm width (2 width units) leave room for adjacent breakers in a crowded panel. The D-curve (10–20× In magnetic trip) is sized for loads with high inrush — motor starters, transformers, or welding equipment — where a B or C curve would nuisance-trip on startup. At 40 A it handles typical branch circuits feeding several small motors or a single larger drive. Breaking capacity is 6 kA per EN 60898 and 10 kA per IEC 60947-2, with a DC rating of 15 kA per IEC 60947-2 at 72 V DC maximum. For UL 1077 / CSA C22.2 No.235 recognition, the interrupting rating is 5 kA. That SCCR headroom means it coordinates cleanly upstream of a 10 kA-rated panelboard without needing a current-limiting fuse ahead of it. The neutral pole is switched (1P+N), so this breaker opens both line and neutral on a fault — important for single-phase sub-circuits where an unswitched neutral would leave the circuit live after trip.
Panel Integration & Environmental Fit
Mounts on a DIN rail via the quick-assembly system — no tools needed for installation or removal. The 36 mm width (2 width units) and 70 mm installation depth fit standard distribution boards and sub-panels. Combined terminals at top and bottom simplify daisy-chaining busbars or ring-tongue wiring. IP20 with connected conductors, plus touch protection on the terminals, means it is safe for open-panel installation where only qualified personnel access the enclosure. Rated for ambient temperature from -40 °C to 75 °C, with humidity derating above 55 °C — suitable for unheated warehouses or outdoor cabinets in temperate climates. Halogen-free and silicon-free construction matters for clean-room or semiconductor-adjacent installations where outgassing from a fault arc could contaminate optics or wafers. Sealable with a lead seal for tamper-evident metering or safety circuits.
Approvals & Compliance
Designed to EN 60898 (6 kA) and IEC 60947-2 (10 kA AC, 15 kA DC). Also carries UL 1077 and CSA C22.2 No.235 recognition at 5 kA, 250 V AC single-phase. Overvoltage category III — suitable for fixed installation downstream of the service entrance. The product designation per DIN EN 61346-2 and DIN EN 81346-2 is letter F (protective device).