The Siemens SENTRON 5SJ4108-8HG42 is a 1-pole miniature circuit breaker rated 8 A at AC with a D tripping characteristic. It occupies one modular width unit (18 mm) and mounts on a standard DIN rail in any position. The D curve means it tolerates high inrush currents — typical for motor or transformer branch circuits where the magnetic trip is set to 10–20× rated current, so nuisance tripping on start-up is less likely than with a B or C curve.
Thermal derating and ambient limits
Rated 8 A at 30 °C and 40 °C without derating. At 45 °C the continuous current drops to 7.8 A, at 50 °C to 7.6 A, at 55 °C to 7.4 A, and at 60 °C to 7.2 A. The operating range spans -40 °C to 75 °C. Pollution degree 3 and overvoltage category 3 suit this breaker for industrial control panels where conductive dust and transient surges are expected. Sealable terminals help lock settings for compliance-sensitive installations.