What it is and what it does
The Siemens 5SY5240-6CC12 is a 2-pole miniature circuit breaker (MCB) from the 5SY5 series, rated for 440 V DC with a 10 kA breaking capacity and a B40 tripping characteristic. That B40 curve means it trips instantaneously between 3 and 5 times rated current — 120 to 200 A — making it a standard choice for protecting DC circuits against short circuits and overloads in control panels and distribution boards.