The Siemens 5SL4201-8 is a 2-pole miniature circuit breaker from the SENTRON series, rated 1 A with a D tripping characteristic and a 10 kA breaking capacity per both EN 60898 and IEC 60947-2. That D-curve means it tolerates the high inrush currents typical of motor loads, transformers, or solenoid banks — the magnetic trip threshold sits higher than a B or C curve, so nuisance tripping on startup is less likely. The 10 kA interrupting rating at 400 V AC tells you it can safely clear a fault up to that level without upstream fuses needing to act first, which simplifies coordination in a distribution board.
DIN-rail fit and panel integration
Two modular-width units wide (36 mm), 76 mm deep, 90 mm tall — it snaps onto standard DIN rail and occupies the same footprint as any other 2-pole SENTRON MCB. Mounting position is unrestricted, so you can orient it vertically or horizontally inside the enclosure without derating the thermal trip. The 70 mm installation depth leaves room behind the busbar stack in a typical 120 mm deep distribution board. IP20 with conductors connected, which is the norm for enclosed panel-mount breakers — not rated for washdown or outdoor exposure. Overvoltage category III and pollution degree 2 confirm it's intended for fixed-installation distribution boards, not portable equipment.
Thermal derating and ambient limits
The 1 A nominal rating holds at 30 °C ambient. At 40 °C it derates to 0.96 A, at 45 °C to 0.94 A, and at 55 °C to 0.9 A. If your panel runs hot — say next to a VFD or transformer — the actual continuous current the breaker can carry without nuisance tripping drops by roughly 4–10 %. The operating range spans -40 °C to 75 °C, so cold starts in unheated enclosures are fine; the storage limit is the same 75 °C maximum.