The Siemens 5SU1656-0KV40 is a combined residual current device and miniature circuit breaker (RCBO) in a single 1+N-pole module. It integrates a Type AC RCD rated at 300 mA residual sensitivity with a B-curve MCB rated at 40 A, all in a 70 mm deep enclosure.
The 300 mA IΔn is a fire-protection level, not a person-protection level — 30 mA is the touch-safe threshold per IEC 60364. This unit goes into circuits where nuisance tripping from normal leakage (long cable runs, IT equipment) would be unacceptable, but where earth-fault fire risk still needs covering. The 6 kA Icn at 230/400 V is the short-circuit capacity the device can safely interrupt — adequate for TN and TT systems with upstream overcurrent protection sized to keep let-through energy within the device's limits.
Integration note
The 70 mm depth is a key fit dimension for shallow enclosures — many standard RCBOs run 75–80 mm deep, so this unit buys an extra 5–10 mm of wiring space behind the DIN rail. The 1+N-pole format (switched phase, solid neutral) is the common European residential/commercial configuration. Terminal capacity and wire range are standard for the class; verify against your gland-plate and busbar layout before committing the panel layout.