What this 40 A B-curve MCB is for
The Siemens 5SL3240-6 is a 2-pole miniature circuit breaker from the SENTRON 5SL3 family, rated 40 A at 400 V AC with a B-curve tripping characteristic. B-curve means it trips at 3–5× rated current — standard for residential and light commercial loads where inrush is modest (lighting, socket circuits, control transformers). The 4.5 kA breaking capacity per EN 60898 and IEC 60947-2 covers most building-distribution fault levels. Two poles switched, no neutral switching — this is a 2P (line/line) breaker for single-phase or two-phase circuits.
Panel fit and wiring
Snaps onto DIN rail — 36 mm wide (2 width units), 76 mm deep, 90 mm tall. Mounting position any, so vertical or horizontal rail layouts work. Terminals accept solid or stranded copper from 0.75 mm² up to 25 mm²; torque to 2.5–3 N·m with a screwdriver. Installation depth 70 mm leaves room behind the rail for wiring channels. IP20 with conductors connected — fine inside a closed panel, not for wet locations.