What it is and what it does
The Siemens 5SL4208-7 is a 2-pole miniature circuit breaker from the SENTRON family, rated 8 A at 400 V AC with a C tripping characteristic. It interrupts fault currents up to 10 kA per EN 60898 and IEC 60947-2 — that means it clears a short-circuit fast enough to protect the downstream wiring and avoid cascading upstream breakers. The C curve (5–10× In) is the standard choice for inductive loads like contactors, small motors, and lighting ballasts in commercial panels; it handles the inrush without nuisance trips while still clearing a hard fault.
Thermal derating and ambient reality
The 8 A rating holds at 30 °C. At 40 °C it derates to 7.39 A, at 45 °C to 7.04 A, and at 55 °C to 6.37 A (–). If this breaker sits in a crowded panel near transformers or drives, that derating curve is the one that governs the load you can actually protect — not the nameplate 8 A. The operating range spans –40 °C to +75 °C (–), so it takes the radiant heat and cold start conditions you see in outdoor or mill-adjacent enclosures.
Panel fit and mounting
Two modular width units (36 mm wide) snap onto standard DIN rail. Depth is 76 mm, installation depth 70 mm. Mounting position is any — no derating for sideways or inverted install. Touch protection is built in. The housing is halogen-free and silicon-free (–), which matters if the panel sits in a clean room or near sensitive electronics where outgassing can cause contact corrosion.