The Siemens 5SL4240-7RC is a 2-pole SENTRON miniature circuit breaker with a C tripping characteristic, rated 40 A and a 10 kA breaking capacity per EN 60898 at 415 V AC. That 10 kA rating means it can safely interrupt a fault current up to 10,000 amps without welding its contacts or failing — enough headroom for most residential and light commercial distribution boards where the prospective short-circuit current stays under that threshold.
At 18 mm wide (one modular width unit), this 2-pole breaker occupies a single 18 mm slot on a standard DIN rail.
The 40 A rating on a 2-pole breaker covers single-phase 40 A circuits or two legs of a three-phase system. Rated operational voltage is 415 V AC, with a maximum of 440 V AC in multi-phase operation. The 10 kA breaking capacity is per EN 60898, the standard for household and similar installations; the same part also carries a 10 kA rating per IEC 60947-2 for industrial applications.