Residual current device

A residual current device is a safety device that disconnects a power circuit whenever it detects an excessive level of earth leakage current (residual current) in the earth conductor (PE). Residual current can be attributed to dangerous contact voltage resulting from an insulation fault. All-pole disconnection takes place within 0.2 seconds.

Residual current devices are available for different rated residual currents. Variants with tripping currents of 30 mA are also used for personal protection. Greater tripping currents primarily provide protection against fires caused by earth leakage current.

Devices with rectifier circuits such as frequency inverters, which in the event of a malfunction can produce DC leakage current, must not be used downstream of standard residual current devices. In this scenario, AC/DC-sensitive residual current devices with higher tripping current are required to prevent unwanted tripping when the drive system is activated.