The Siemens 5SU1654-1KV25 is an FI/LS combination unit — an RCBO that packs both residual-current and overcurrent protection into one 70 mm wide, 1+N-pole package. Type AC detection means it trips on sinusoidal AC earth faults; the 300 mA IΔn is sized for circuits where a lower threshold would nuisance-trip (lighting, general sockets in commercial or industrial distribution boards). The C-curve 25 A thermal-magnetic characteristic handles moderate inrush from motorised loads or fluorescent banks without dropping out on start-up.
Rated breaking capacity and coordination
Breaking capacity is 10 kA per IEC 60898-1. That is the fault-current ceiling the device can safely interrupt — sized for most commercial and light-industrial final circuits where the prospective short-circuit current stays under 10 kA. If your distribution board's upstream fault level exceeds that, the 5SU1654-1KV25 needs a current-limiting backup fuse or MCB ahead of it; a 16 A gG or similar will keep let-through energy within the device's rating.
Panel integration
The 70 mm width matches the standard Siemens FI/LS module footprint — clips onto the DIN rail, occupies two 17.5 mm modular spaces plus the neutral pole width. Phase and neutral conductors terminate under captive screws; the outgoing neutral is internal to the unit, so no separate N-terminal block needed downstream. For a 25 A C-curve RCBO, check the ambient temperature inside the enclosure: above 40 °C, the thermal trip threshold shifts, so either derate or leave ventilation slots clear.