The Siemens SENTRON 5SL6140-6YA is a 1-pole miniature circuit breaker with a B tripping characteristic, rated 40 A at 30 °C and 400 V AC.
The 40 A rating at 30 °C is the headline figure, but the derating curve matters in a warm panel: at 40 °C ambient the breaker is rated 0.96 A (a clear data anomaly — likely a misprint for a different variant; the 45 °C figure of 37.2 A is more plausible for this class). In practice, size the continuous load at no more than 32 A in a 40 °C enclosure to avoid nuisance tripping. The B curve (3–5× In) gives fast magnetic trip for short circuits while passing normal inrush from lighting and control transformers.
Occupies 1 modular width unit (18 mm). Mounting position is any. IP20 rating applies with distribution board cover fitted.