What it is and what it does
The Siemens SENTRON 5SM9626-6 is an electronic residual current (RC) unit designed as a companion for the 5SL4 miniature circuit breaker series. It provides earth leakage protection in a 2-pole, Type A configuration, rated at 63 A with a 300 mA tripping threshold, on a 230/400 V AC supply at 50 Hz. The Type A classification means it detects sinusoidal AC residual currents plus pulsating DC residual currents — the typical waveform from rectifiers, variable-speed drives, and switching power supplies found in commercial and light industrial panels. The instantaneous design means it trips without intentional delay, which is the correct choice for general-purpose socket-outlet circuits and equipment protection where selectivity against transient surges is not required.
Mounting and integration
Mounts on standard DIN rail (35 mm), occupying 2 width units (36 mm). The 70 mm installation depth matches the 5SL4 MCB it couples with, so the assembly sits flush in the distribution board. The supply feed is from the top, above the miniature circuit breaker — maintain that orientation for correct wiring. Terminal torque is 2.5 to 3 N·m; the screw terminals accept solid conductors from 0.75 to 35 mm² and stranded from 0.75 to 25 mm², covering most downstream circuit sizes up to the 63 A rating. IP20 rating applies once the distribution board is installed with conductors connected — this is an enclosed-panel device, not for wet or outdoor locations.
Key ratings in context
The 300 mA residual tripping current is a common threshold for fire protection and equipment-level leakage detection, rather than personnel protection (which typically uses 30 mA). The 3 kA surge current resistance means the unit can withstand transient overcurrents from switching events or lightning-induced surges without nuisance tripping — important on supply networks with known surge activity. Overvoltage category III confirms suitability for fixed-installation distribution boards downstream of the main service entrance. The 10 000 mechanical switching cycles typical service life aligns with the coupled MCB's endurance for normal panel operation.