What this part is and what it does
The Siemens 5SM9426-0 is a SENTRON residual current (RC) unit — the electronic trip module that pairs with a 5SL4 miniature circuit breaker to form a combined RCD/MCB (RCBO) assembly. It is a 2-pole, type AC device rated at 63 A with a 100 mA residual tripping threshold, supplied at 230/400 V AC. The type AC designation means it detects sinusoidal AC fault currents only; it is not rated for pulsating DC or smooth DC faults, so the application must be purely AC residual load.
Mounting and integration into the panel
Mounts on standard DIN rail (35 mm) in any position. The unit occupies 2 width units (36 mm) and has an installation depth of 70 mm. It clips to the top of a 5SL4 miniature circuit breaker — the supply feeds in from above, through the RC unit, then to the MCB below. The assembly fits enclosures meeting DIN 43880 size 1. Terminal torque is 2.5 to 3 N·m. The IP20 rating applies only when the distribution board is installed with conductors connected — bare units on the bench are not touch-safe.
Wire sizing and termination
Accepts solid conductors from 0.75 to 35 mm² and stranded conductors from 0.75 to 25 mm². This range covers most sub-main and feeder circuits up to 63 A. The screw terminals are rated for the full 63 A continuous current without derating at the 55 °C ambient upper limit.