The Siemens 5SM1616-6 is a SENTRON 5SM1-series residual-current circuit breaker (RCCB) — two poles, Type A instantaneous trip, rated 63 A at 230 V AC with a 300 mA residual trip threshold. That 300 mA trip is a common choice for general protection in distribution boards where you need earth-leakage detection but want to avoid nuisance tripping on normal leakage from filters or long cable runs.
Ratings that matter for the panel
Mounts on DIN rail (REG), any position, and takes 2 width units (about 36 mm at 18 mm per unit). Installation depth is 55 mm — fits standard enclosures without crowding the gland plate. Terminal torque: 2.5 to 3 N·m on the screw terminals, which accept solid or stranded copper from 1 to 16 mm². That range covers most distribution tails and sub-feed conductors you'd see downstream of a 63 A breaker.
Thermal derating — the real-world current limit
The 63 A rating holds at ambient up to 45 °C. Above that, the continuous current drops: 60.48 A at 50 °C, 57.96 A at 55 °C, 55.44 A at 60 °C, 52.92 A at 65 °C, and 50.4 A at 70 °C. The storage range (-40 to +60 °C) is wider, but that's handling, not running.