The Siemens 5SM1644-6FD is a Type A FI-Protector (residual current device / RCD) rated 40A, 4-pole, with a rated residual current IΔn of 0.3A at 400V. The 55mm width and 4TE modular width fit standard DIN-rail distribution boards. Type A detection handles pulsating DC fault currents common in modern electronics loads — not just sinusoidal AC.
Application Context
Mounts on 35mm DIN rail in a standard distribution board or sub-distribution panel. The 4TE width (approx 70mm) occupies four modular slots. Rated for 400V phase-to-phase systems, 4-pole switching covers three phases plus neutral for TN or TT systems. Type A RCD is specified where loads generate pulsating DC fault currents — think single-phase rectifiers, switched-mode power supplies, LED drivers, or variable-speed drives with front-end rectifiers.
Part of the Siemens 5SM series FI-Protectors. Standard compliance documentation (declaration of conformity, CE marking) is available from Siemens for this product line. The Type A designation follows IEC/EN 61008 / IEC/EN 62423 requirements for residual current devices.