The Siemens 5SU1354-0KV20 is a combined residual-current device (RCD) and miniature circuit breaker (MCB) — an FI/LS-protector — in a single 1+N-pole module.
Where it goes in the panel
The 1+N-pole format (switched phase plus switched neutral) means it occupies a single module width — 70 mm deep, per the description — and the neutral pole opens with the phase, which is required in some regional wiring regulations for RCD-protected circuits. The Type AC designation limits it to sinusoidal AC residual currents; if the downstream load includes electronics with half-wave rectification (e.g., switched-mode power supplies, LED drivers, variable-speed drives), a Type A or Type F device would be needed to detect pulsating DC fault currents that Type AC cannot see.