What it is and what it does
The Siemens 5SL6540-6 is a SENTRON miniature circuit breaker (MCB) with a 1P+N pole configuration, meaning it switches both the line and neutral conductors. It's rated 40 A at 30 °C with a B tripping characteristic — the B curve trips between 3 and 5 times rated current, making it the standard choice for residential and light commercial lighting and socket-outlet circuits where inrush is low. The breaking capacity is 6 kA per both EN 60898 and IEC 60947-2, which covers the majority of domestic and infrastructure distribution boards.
What the ratings mean for fit
The 40 A rating is the continuous current at 30 °C ambient. It derates to 37.57 A at 40 °C and 33.61 A at 55 °C — if your panel runs hot, factor that in. The B curve (3–5× In) is deliberate: it avoids nuisance trips on lighting and general-purpose loads but will not hold motor inrush; for motor circuits you want C or D curve. The 6 kA breaking capacity is the maximum prospective fault current the breaker can safely interrupt — adequate for most residential and commercial sub-distribution, but verify your available fault current at the panel. Overvoltage category III and pollution degree 2 confirm it's rated for fixed-installation downstream of the main distribution board.
Where it goes and how it mounts
Snaps onto standard 35 mm DIN rail. Width is 36 mm (2 modular units), depth 76 mm, installation depth 70 mm. The neutral conductor is switched internally — no separate neutral bar needed downstream of this breaker. Mounting position is any orientation. Touch protection is built in. Sealable with a lead seal if the installation requires tamper evidence. Halogen-free and silicon-free construction matters for environments sensitive to outgassing, like clean rooms or certain industrial zones.