Protection against electric shock using residual current devices in circuits with electronic equipment

One of the means of protection in the case of fault in low voltage systems is automatic disconnection of supply. Automatic disconnection of supply is required where a risk of harmful pathophysiological effects on humans can arise, resulting from dangerous touch voltage. In order to fulfil this requirement residual current devices (RCDs) are used as protective devices. In circuits with electronic equipment various frequencies and distorted earth fault current can occur. The analysis indicates that earth fault current frequency other than the rated value often causes improper operation of RCDs. In some cases the protective device cannot trip at all and thus protection against electric shock is not effective. In circuits with electronic equipment transient and steady state leakage current can occur so it causes the RCDs unwanted tripping. This paper presents special problems of selection and operation of RCDs in circuits with electronic equipment, based on the laboratory and field investigations.