The Siemens 5SU1654-1KV20 is a combined residual-current and miniature circuit breaker (RCBO) — an FI/LS-protector in Siemens' 5SU1 range. It combines Type AC (wave shape) residual-current detection at 300 mA with a C-curve 20 A overcurrent trip and 10 kA breaking capacity in a 1+N-pole, 70 mm wide housing.
The 300 mA sensitivity (IΔn) is the trip threshold for earth leakage — it's a fire-protection level, not the 30 mA needed for personal shock protection. This suits sub-distribution boards supplying fixed equipment where the leakage budget is tight enough that a 30 mA device would nuisance-trip. The C-curve (C 20 A) means the magnetic trip fires at 5–10× In (100–200 A), so it handles motor inrush and transformer energization without dropping out.
Panel integration
The 70 mm width (4 module spaces on a DIN rail) is wider than a standard single-pole MCB — account for the space when laying out the distribution board. The 1+N-pole configuration switches the line conductor and provides neutral disconnection; the neutral pole is switched internally, so a separate neutral bar connection is not needed. Type AC detection handles sinusoidal AC residual currents only — not pulsed DC or smooth DC, so verify the load type does not produce rectified leakage (e.g., from variable-speed drives, LED drivers, or UPS-fed circuits).