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Residual current devices

Residual current devices afford fault protection (formerly referred to as: protection in case of indirect contact) and supplementary protection (formerly referred to as: protection in case of direct contact) in low-voltage systems. In the event of a basic insulation failure or direct contact with live components, they provide some degree of protection to persons, material assets and livestock against harm.

Operating principle of a residual current device

In fault-free electrical installation, the vector sum of the load currents of all connected conductors equals zero. A residual current occurring in the protected circuit as the result of an insulation fault, for example, induces a voltage in the secondary winding of a summation current transformer. The evaluation electronics system monitors the induced voltage and transmits a trip command to the RCD trip unit if the trip criterion is fulfilled. The molded case circuit breaker with residual current protection combination is designed to ensure that the molded case circuit breaker contacts open if the residual current exceeds a preset value.