What the ratings mean for fit
The 5SY8550-8 is a Siemens SENTRON miniature circuit breaker (MCB) in a 2-pole 1P+N configuration with neutral conductor switching. Its D tripping characteristic — 10 to 20 times rated current — is sized for high-inrush loads: motor starters, transformers, or welding equipment where a B- or C-curve would nuisance-trip on startup. The 50 A rating at 45 °C (48.75 A at 50 °C, 47.45 A at 55 °C) means you size the breaker for the actual ambient in the enclosure, not the nameplate. Breaking capacity is 20 kA per IEC 60947-2 (15 kA DC, 5 kA per UL 1077/CSA C22.2 No. 235) — enough for most industrial panelboards with a 10 kA or higher available fault current at 400 V. Mounts on DIN rail via the quick-assembly system, any position, with an installation depth of 70 mm and overall depth of 76 mm. The 36 mm width (2 modular units) fits standard distribution boards. IP20 with connected conductors — suitable for dry indoor panels, not washdown zones. Pollution degree 3 and overvoltage category III mean it's rated for industrial environments with conductive pollution and transient overvoltages up to 4 kV.
Compliance and documentation
Rated per IEC 60947-2 and UL 1077/CSA C22.2 No. 235. Halogen-free and silicon-free construction. Sealable for lockout/tagout. Vibration resistance per IEC 60068-2-6: ±1 mm at 5–25 Hz, 50 m/s² at 25–150 Hz. Ambient temperature range -40 °C to 75 °C, with humidity derating above 55 °C.