The Siemens SENTRON 5SU9404-1KK10 is an RCD-operated circuit breaker (RCBO) — it combines overcurrent protection and residual current detection in a single 18 mm wide module.
The 10 A rating is at 30 °C ambient; at 40 °C it derates to 9.4 A, at 45 °C to 9.1 A, at 50 °C to 8.7 A, and at 55 °C to 8.1 A. If the panel runs warm — common in a crowded DIN-rail enclosure — the actual continuous current the RCBO can carry without nuisance tripping is lower than the label. It is a 1P+N device (switched phase, solid neutral) that detects AC-type fault currents only — not pulsed DC or smooth DC. If the downstream load includes variable-speed drives, LED drivers, or any rectifier front end, an AC-type RCD may not trip on the residual DC content; that application calls for a Type A or Type B RCBO.
Occupies one 18 mm width unit on a standard DIN rail. The power supply can enter from either the top or bottom, which simplifies busbar alignment in pre-wired boards. Touch protection is built into the terminals. IP20 rating applies only when the distribution board is installed and conductors are connected — the RCBO itself is not splash-proof. Mounting position is unrestricted.