Integrator's spec recap
The Siemens SENTRON 5SY4540-7 is a 2-pole (1P+N) miniature circuit breaker rated 40 A at 35 °C with a C tripping characteristic. It snaps onto a DIN rail via the quick assembly system and occupies 2 modular width units (36 mm wide). The 10 kA breaking capacity per EN 60898 covers most residential and light commercial panelboards; the 15 kA rating per IEC 60947-2 gives headroom for industrial distribution where the prospective fault current is higher. The C-curve means the magnetic trip operates at 5 to 10 times In, so it handles moderate inrush from motor starters or transformers without nuisance tripping, but still clears a hard short fast enough for cable protection.
Thermal derating and ambient limits
The 40 A rating holds at 35 °C. At 45 °C the continuous current drops to 36.28 A; at 50 °C it is 34.96 A; at 55 °C it is 33.6 A; at 60 °C it is 32.16 A. If the panel internal ambient runs above 35 °C, size the upstream protection for the derated value, not the nameplate 40 A. The breaker operates from -40 °C to 75 °C ambient. Humidity must be managed: max 95% up to 55 °C, then derated to 55% at 70 °C and 35% at 75 °C. In a sealed enclosure with high moisture load, factor that into the ventilation design.
Mounting and integration
Mounts in any position on a DIN rail. The installation depth is 70 mm; overall depth is 76 mm. Combined terminals at top and bottom accept copper conductors. The IP20 rating applies with connected conductors — suitable for enclosed panelboards, not for wet-area standalone use. Pollution degree 3 and overvoltage category III mean the breaker is rated for fixed installations inside industrial enclosures where conductive pollution may occur, not just clean residential panels.