What this RCBO does on the rail
The Siemens 5SU9604-1KK25 is a 1P+N RCD-operated circuit breaker from the SENTRON 5SU9 family — a combined residual-current device and overcurrent protector in a single 18 mm wide module. Energy limiting class 3 keeps let-through energy low, which helps with downstream device coordination in a distribution board.
Derating and thermal reality
At 40 °C it derates to 23.5 A, at 45 °C to 22.75 A, and at 50 °C to 21.75 A — so in a warm enclosure (common in a packed panel) you lose roughly 3 A off the nameplate. Storage range is wider (-40 to +75 °C) for spares sitting on a shelf. Power dissipation is only 0.75 W at rated load, so heat buildup in a multi-way board is manageable.
Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm², covering everything from 1.5 mm² lighting circuits up to 6 mm² or 10 mm² feeder tails. Touch protection is built in (IP20 with conductors connected, per the spec).