Background Leakage Current (Cumulative Leakage — Large Installation)

The sum of the small, normal leakage currents to earth continuously produced by each individual device fitted with an EMC suppression filter (variable frequency drives, IT equipment, LED drivers, switch-mode power supplies), which, with a large number of devices connected within the same installation, can add up to a substantial total leakage current — even without any actual earth fault being present. When this cumulative background leakage current reaches a substantial fraction of the rated residual current of an upstream RCD, it can cause nuisance tripping at the slightest additional leakage current, or reduced sensitivity to genuine earth faults. Control is achieved by spreading leakage current over several selectively switched RCD groups instead of a single central RCD, and by accounting at the design stage for the summed manufacturer-stated leakage current of each connected device.