What this 40 A C-curve MCB is and where it fits
The Siemens 5SL1240-7MB is a 2-pole miniature circuit breaker from the SENTRON family, rated 40 A with a C tripping characteristic. It protects branch circuits in residential and infrastructure panels against overload and short-circuit faults up to 3 kA per IEC 60947-2 at 230/400 V AC. The C-curve means the magnetic trip operates at 5 to 10 times rated current — suited for moderate inrush loads like small motors, transformers, and lighting banks where a B-curve would nuisance-trip but a D-curve is unnecessary.
Panel fit and mounting constraints
Occupies 2 modular width units (36 mm) on a DIN rail, with a depth of 76 mm and an installation depth of 70 mm behind the panel surface. Mounting position is unrestricted, and the IP20 rating with connected conductors is standard for enclosed distribution boards. Sealable design allows the installer to lock the toggle position — useful for compliance with local isolation rules or to prevent unauthorized reset on a critical circuit.
Environmental and compliance profile
Halogen-free and silicon-free construction, rated for ambient temperatures from -40 °C to 75 °C. Overvoltage category III and pollution degree 2 suit fixed-installation mains circuits.