The Siemens 5SU1356-1DA25 is a combined residual current device and miniature circuit breaker (RCBO) — what Siemens calls an FI/LS protector. It packs Type AC earth-leakage detection at 30 mA rated residual current (IFN) and a 6 kA breaking capacity into a single 1+N-pole module with a C-curve 25 A overcurrent trip.
What the ratings mean for fit
Type AC detection means it trips on sinusoidal AC residual currents only — the standard choice for general-purpose circuits feeding resistive and inductive loads like heaters, motors, and lighting where no pulsed or DC fault currents are expected. The 30 mA sensitivity is the common touch-protection threshold; it covers the human body path to ground in a fault. The 6 kA breaking capacity (Icn) is the short-circuit rating at the device's rated voltage — adequate for most residential and light commercial sub-distribution boards where the prospective fault current at the board is known to be under 6 kA. The C-curve (25 A) means the magnetic trip operates at 5 to 10 times rated current, so it holds through motor inrush and capacitive loads without nuisance tripping.
Where it goes in the panel
This is a 1+N-pole unit — it switches and protects the line conductor and switches the neutral, but the neutral is not overload-protected. The pigtail connection (factory-fitted neutral tail) simplifies wiring in DIN-rail distribution boards: the neutral bus bar connects to the pigtail, and the line side clips onto the bus bar or is fed from the upstream device. The 70 mm depth (D=70mm) is standard for Siemens 5SU series RCBOs, so it fits flush in a standard enclosure without protruding past the cover.