The Siemens 5SU1656-7KK25 is a SENTRON-series RCBO (residual current circuit breaker with overcurrent protection) combining a 25 A overcurrent trip (C-curve, 1P+N) with a 300 mA Type A residual current device in a single 2-module-width package. It is rated for 6 kA breaking capacity per EN 60898, making it suitable for final subcircuit protection in residential and commercial distribution boards where both overcurrent and earth-fault protection are required in one device.
Ratings and what they mean for fit
The 25 A rating at 30 °C is the headline thermal current; at elevated panel temperatures the device derates — 23.5 A at 40 °C, 21.75 A at 50 °C, and 18.25 A at 70 °C. If the distribution board sits in a warm environment (e.g., adjacent to a boiler or in a non-climate-controlled enclosure), use the 40 °C or 50 °C column for sizing, not the 30 °C figure. The 300 mA residual current rating and Type A classification mean the device detects sinusoidal AC fault currents and pulsating DC fault currents (common from rectified loads like switching power supplies, LED drivers, and variable-speed drives). It is not suitable for smooth DC fault currents — that would require Type B. For general-purpose final circuits with electronic loads, Type A is the standard choice. The C-curve (tripping characteristic class C) means the magnetic trip operates at 5 to 10 times rated current, so it handles moderate inrush from motorized loads (pumps, fans, compressors) without nuisance tripping, while still providing short-circuit protection. The 6 kA breaking capacity (per EN 60898) is adequate for most domestic and light commercial installations where the prospective short-circuit current at the board is under 6 kA.
Integration and mounting
The device occupies 2 modular width units (36 mm) on a DIN rail, with a depth of 77 mm and installation depth of 70 mm. It mounts in any position and accepts supply from either top or bottom. The IP20 rating applies when installed in a distribution board with connected conductors — meaning the board enclosure provides the environmental seal; the RCBO itself is finger-safe but not splash-proof.