The Siemens 5SU1644-8RC32 is a 4-pole RCBO rated at 32 A with D characteristic and Type A residual current protection at 300 mA. It occupies 7 module widths on a DIN rail, sized for a three-phase plus neutral circuit where you need both overcurrent and earth-leakage protection in one device. The D curve means it tolerates high inrush currents — think motor starts, transformer energisation, or welder loads — without nuisance tripping, while the 300 mA Type A residual trip catches pulsating DC fault currents that a standard AC type would miss.
What the ratings mean for fit
The 32 A rating governs the continuous load the RCBO can carry — sized for a 32 A final subcircuit feeding a motor group, a small distribution board, or a piece of fixed equipment. The D characteristic (10–20× In magnetic trip) is the deciding factor for fit: it avoids tripping on the inrush of a 7.5 kW DOL motor or a bank of discharge lamps, where a C-curve device would nuisance-trip. The 300 mA Type A residual element provides earth-fault protection for circuits with electronics or rectified loads — VFDs, UPS systems, or LED drivers — that generate smooth DC fault currents an AC-only RCD cannot detect.
Panel integration
Four-pole RCBO in a 7-module housing snaps onto standard 35 mm DIN rail. The 4-pole format covers L1, L2, L3, and N — the neutral is switched and monitored for residual current. At 7 modules wide, it fills about 125 mm of rail; plan for that footprint in a sub-distribution board or a motor control centre. Spring-cage terminals accept 0.2–2.5 mm² solid or ferruled stranded conductors.