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.
What the ratings mean for fit
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. The 10 kA breaking capacity (Icn) is the fault current it can safely interrupt at the rated voltage — adequate for most residential and light commercial distribution boards, but check the prospective short-circuit current at the installation point.
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).