Miniature circuit breaker, D curve, 2-pole — what the ratings mean for fit
The Siemens SENTRON 5SY4540-8 is a 2-pole (1P+N) miniature circuit breaker with a D tripping characteristic, designed for mechanical engineering and industrial panel applications. Its D curve means it tolerates high inrush currents — typically 10 to 20 times rated current — making it the right choice for motor, transformer, and capacitor bank branch protection where nuisance tripping on startup is the main concern. Breaking capacity is 10 kA per IEC 60898-1 and 15 kA per IEC 60947-2, with an additional 15 kA at DC per IEC 60947-2. For UL 1077 / CSA C22.2 No.235 installations, the interrupting rating is 5 kA. That spread covers most industrial distribution panels; the 15 kA IEC figure gives headroom for higher-fault locations without cascading upstream. Rated operational voltage is 230 V AC (single-phase, 250 V max) and 60 V DC (72 V max). The neutral conductor is switched (1P+N), which is standard for final subcircuits where both line and neutral need isolation. Mounting position is any, and the 2-module-width (36 mm) footprint snaps onto standard DIN rail — no special adapters.
Standards and environmental ratings
Designed and certified to IEC / EN 60898-1 and IEC / EN 60947-2, plus UL 1077 for North American acceptance. Overvoltage category III, pollution degree 3. Halogen-free and silicon-free construction, important for sensitive environments (semiconductor fabs, medical device assembly) where outgassing can contaminate optics or contacts. Ambient temperature range is -40 °C to +75 °C, with humidity limits of 95% at 55 °C, derating to 35% at 75 °C. Vibration resistance per IEC 60068-2-6: ±1 mm at 5 to 25 Hz, 50 m/s² at 25 to 150 Hz — adequate for machine-mounted panels near rotating equipment.
Physical integration and wiring
Dimensions: 76 mm depth, 36 mm width (2 MW), 90 mm height. Installation depth is 70 mm. Combined terminal at top and bottom. Mechanical service life is 10,000 operating cycles typical.