50 A D-curve MCB for industrial branch circuits
The Siemens 5SY7550-8 is a 2-pole (1P+N) miniature circuit breaker from the SENTRON 5SY7 series, rated at 50 A with a D tripping characteristic. The D-curve means it tolerates inrush currents 10–20 times the rated current — designed for loads with high starting surges like small motors, transformers, or solenoid banks where a B- or C-curve would nuisance-trip on startup. The 15 kA breaking capacity per IEC 60898 and IEC 60947-2 means it can safely interrupt fault currents up to that level without upstream cascading, making it suitable for industrial sub-distribution boards where fault current is substantial. Rated at 230 V AC, this breaker snaps onto a DIN rail via the quick-assembly system and can be mounted in any position — no derating for upside-down or horizontal orientation. The IP20 rating (with connected conductors) is standard for enclosed panel use; the breaker is not intended for wet or washdown environments without an outer enclosure.
DIN-rail footprint and terminal capacity
The 5SY7550-8 occupies 36 mm width (2 width units) on the DIN rail, with a depth of 76 mm and height of 90 mm. Installation depth is 70 mm — account for this when planning gland-plate clearance and door swing in the enclosure. Combined terminals top and bottom accept solid or stranded conductors from 0.75 mm² up to 35 mm², covering most panel wiring from control circuits to feeder cables. The terminals are sealable and touch-protected, meeting the requirements for panel builders who need to lock out unauthorized access after commissioning. Halogen-free and silicon-free construction matters for environments where outgassing from a fault could damage sensitive electronics or where silicone contamination affects paint adhesion or optical sensors — common in automotive paint shops or semiconductor fabs.
Environmental range and compliance
Ambient temperature range spans -40 °C to +75 °C, with humidity limits of 95% at 55 °C, derating to 35% at 75 °C. This covers unheated outdoor cabinets in cold climates as well as warm switchgear rooms. Overvoltage category III means it is rated for fixed installation downstream of the main distribution board, not for point-of-use equipment. The part is classified per DIN EN 61346-2 and DIN EN 81346-2 as function F (protective device).