What it is and what it does
The Siemens 5SU1354-3KK25 is a 2-pole (1P+N) RCBO from the SENTRON 5SU1 series, combining overcurrent protection and residual current detection in a single 36 mm wide unit. It's rated 25 A at 30 °C with a B tripping characteristic, and a Type F fault current sensor — designed for circuits where variable-speed drives or frequency converters may generate smooth DC or mixed-frequency leakage currents that standard AC or A types might miss. Breaking capacity is 10 kA per EN 60898 at 230/240 V AC, overvoltage category III, pollution degree 2. The unit is rated for 50/60 Hz and can be fed from either top or bottom. Energy limiting class 3 means it limits let-through energy well enough for most downstream equipment protection.
Thermal derating — what the numbers mean
The 25 A rating holds only at 30 °C ambient. At 40 °C it's 23.5 A, at 50 °C it's 21.75 A, and at 60 °C it drops to 20.25 A. By 70 °C you're down to 18.25 A. If this RCBO sits in a crowded enclosure near other heat sources, use the derated value — not the 25 A nameplate — for your load calculation.
Mounting and integration
Occupies 2 width units (36 mm) on a DIN rail, installation depth 70 mm, overall depth 77 mm. Mounting position is any — no restriction on upright or sideways. IP20 with conductors connected and distribution board installed. Halogen-free and silicon-free construction for environments sensitive to outgassing.