RCBO for final-circuit protection with combined overcurrent and residual current
The Siemens 5SU1656-0KK20 is a SENTRON RCBO (residual current circuit breaker with overcurrent protection) combining a B-curve miniature circuit breaker and a 30 mA AC-type residual current device in a single 2-module-wide (36 mm) housing. Rated 20 A at 30 °C, it protects final circuits against overload, short-circuit, and earth faults in one unit — saving a DIN-rail position versus separate MCB + RCCB. The B-curve tripping characteristic (3–5 × In) makes it suitable for resistive and general-purpose loads where inrush is modest — lighting circuits, socket outlets, small appliances. The 30 mA AC-type residual current detection handles sinusoidal earth faults, the most common type in residential and light commercial installations. Breaking capacity is rated 6 kA per EN 60898 and 15 kA per IEC 60947-2, giving the panel designer flexibility to apply it under either standard. The higher 15 kA rating under IEC 60947-2 provides additional fault-current headroom for industrial distribution boards where prospective short-circuit currents may exceed 6 kA.
Thermal derating and mounting flexibility
Rated current is temperature-dependent: 20 A at 30 °C, derating to 18.8 A at 40 °C, 17.4 A at 50 °C, 16.2 A at 60 °C, and 14.6 A at 70 °C. In a crowded enclosure with elevated ambient, apply the derated value — the 40 °C figure (18.8 A) is the practical design limit for most panel environments. Mounting position is unrestricted (any orientation), and supply can enter from either top or bottom — simplifies busbar routing and panel layout. The 2 MW (36 mm) width matches standard SENTRON modular spacing; depth is 77 mm, installation depth 70 mm. IP20 protection applies when installed in a distribution board with connected conductors — standard for enclosed panel mounting. Halogen-free and silicon-free construction suits environments sensitive to outgassing, such as clean rooms or telecom shelters.