The Siemens 5SU1353-1KV20 is a combined residual-current device and miniature circuit breaker (RCBO) — an FI/LS protector in Siemens terminology — in a 1+N-pole form factor. It carries a C-curve 20 A thermal-magnetic trip and a 30 mA residual-current (Type AC) detection coil, with a 4.5 kA short-circuit breaking capacity. The 70 mm depth fits standard Siemens distribution boards and sub-distribution panels where space is tight on the DIN rail.
The 30 mA residual-current sensitivity is the standard for personal shock protection in residential and commercial final circuits per IEC 60364. The 4.5 kA breaking capacity (Icn) is the rated short-circuit capacity per EN 61009-1 — adequate for most domestic and light commercial sub-distribution boards where the prospective short-circuit current at the point of installation is below 4.5 kA. In industrial panels or closer to the transformer, a 6 kA or 10 kA device may be required to maintain selectivity.