What this RCBO is and what the ratings mean for your panel
The Siemens SENTRON 5SU9404-0KK32 is an RCD-operated circuit breaker — an RCBO — combining overcurrent protection and residual current detection in a single 18 mm wide module. Rated 32 A at 30 °C ambient with a B tripping characteristic, it clears overcurrents between 3 and 5 times rated current, which is the standard choice for general-purpose lighting and socket-outlet circuits in residential and commercial distribution boards. The 10 kA breaking capacity per EN 60898 and IEC 60947-2 means it can safely interrupt fault currents up to that level without upstream cascading, making it suitable for installation downstream of a larger main breaker in a typical TN or TT system. The 1P+N configuration switches the live pole and provides a switched neutral, which is common in single-phase final circuits across European and Middle Eastern markets.
Thermal derating and conductor sizing
The 32 A rating holds at 30 °C ambient. At 40 °C it derates to 30.08 A, at 45 °C to 29.12 A, at 50 °C to 27.84 A, and at 55 °C to 25.92 A. If the panel ambient runs above 30 °C — common in a crowded enclosure — the actual load must be capped at the derated figure. The terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm², which covers everything from 1.5 mm² lighting circuits up to 10 mm² feeder tails. The installation depth is 70 mm, and the overall depth is 77 mm, so it fits standard 18 mm DIN-rail enclosures with a 70 mm deep back box. Mounting position is unrestricted, and the supply can enter from either top or bottom.
Compliance and approvals
Rated breaking capacity is certified to EN 60898 (10 kA) and IEC 60947-2 (10 kA). Overvoltage category III means it is rated for fixed installation downstream of the main distribution board, not for equipment-level protection. The IP20 rating applies when installed in a distribution board with conductors connected — standard for enclosed panel use. Touch protection is provided on the terminals. The product is assigned function code F per DIN EN 61346-2 and DIN EN 81346-2, which classifies it as a protective device.