What it is and where it fits
The Siemens 5SY5240-7KK11 is a 2-pole miniature circuit breaker from the SENTRON family, with a C-curve tripping characteristic and a rated AC voltage of 400 V. It snaps onto a DIN rail via the quick assembly system and fits any mounting position, so it drops into standard distribution panels without extra hardware. The 36 mm width (2 modular units) and 76 mm depth leave room for adjacent breakers in a crowded enclosure.
Breaking capacity and duty
Rated breaking capacity is 10 kA per EN 60898 and 15 kA per IEC 60947-2 at DC. The C-curve (tripping between 5 and 10 times rated current) handles moderate inrush from motor starters or transformer banks without nuisance trips. Overvoltage category III and pollution degree 3 mean it's rated for fixed-installation panels, not just final circuits.