In DC circuits, arc extinction is harder than AC because there is no natural zero-crossing; the 2-pole design switches both lines, doubling the arc gap. Rated 40 A, it holds the continuous current in a 40 °C ambient without nuisance tripping. The operating voltage maxes out at 500 V DC, so stay at or below that; polarity must be observed on this unit (noted as 'consider polarity' in the specs).
Physical fit and mounting
The 5SY5240-7CC 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 face. That is a standard footprint — drops into any SENTRON or third-party distribution board that accepts 2-MU breakers. The 'quick assembly system' fastening means it snaps onto the rail and can be removed with a screwdriver without disturbing adjacent units. Sealable with a lead seal if the application requires tamper evidence.