Siemens 5SM1646-6BA RCD Type A, 63A 4P 300mA 400V

The Siemens 5SM1646-6BA is a 4-pole residual current device (RCD) rated 63 A at 400 V, with a 300 mA (0.3 A) rated residual operating current. The Type A designation means it detects sinusoidal AC residual currents plus pulsating DC residual currents — the standard requirement for circuits supplying single-phase rectifiers, switching power supplies, or variable-speed drives where pure AC detection is insufficient. The 63 A rating covers the main feeder or sub-distribution board; the 300 mA sensitivity is typical for fire protection or equipment protection rather than direct personal shock protection (which would require 30 mA or lower). The 4TE (4 module widths) form factor snaps onto standard DIN rail, occupying four 18 mm slots in the enclosure.