The 5SM1647-6BA: The 80 A rating means it handles the full load of a three-phase sub-distribution board feeding motor or mixed loads up to that current. The 0.3 A IΔn (300 mA) is a common choice for fire protection in industrial panels — it allows normal leakage from drives and filters without nuisance tripping, while still providing ground-fault detection. Type A detection covers pulsating DC fault currents, which covers most modern electronic loads (VFDs, switched-mode supplies). The 4-pole (3P+N) construction protects all three phases plus neutral in a TN or TT system.
The 4 TE width (roughly 72 mm) means it takes four module positions in a distribution board — plan the gland plate and busbar routing accordingly. Rated for 400 V line-to-line, so it fits European-style 400/230 V three-phase networks.