What it is and what it does
The Siemens 5SL4440-6 is a SENTRON miniature circuit breaker (MCB) with four poles, rated 40 A at 400 V AC and a B tripping characteristic. The B curve means it trips between 3 and 5 times rated current — the standard choice for resistive and general-purpose loads in residential and light commercial panels where inrush is low. Breaking capacity is 10 kA per both EN 60898 and IEC 60947-2, so it can safely interrupt fault currents up to that level without upstream coordination changes in most distribution boards.
Mounting and integration
Snaps onto standard DIN rail (4 modular width units, 72 mm wide). Depth is 76 mm, installation depth 70 mm — fits flush in most enclosures without extra gland-plate clearance. Mounting position any, so vertical or horizontal rail orientation works. IP20 with connected conductors; suitable for enclosed distribution boards where the front cover provides the real ingress protection.
Thermal derating and environment
Rated 40 A at 30 °C; derates to 37.89 A at 40 °C and 34.47 A at 55 °C. Ambient range -40 to 75 °C covers unheated utility rooms and outdoor-rated enclosures. Halogen-free and silicon-free construction — relevant for clean-room or corrosive-environment installations where outgassing matters. Sealable, so the toggle can be locked in the off position for lockout/tagout.