Residual current device with high immunity to nuisance tripping

Residual current devices, though offering a high degree of protection from fire and electric shock hazards, are notoriously prone to nuisance tripping. Efforts have been made to counter the problem primarily by the use of simple time delays, with a moderate degree of success. This paper presents two techniques that greatly reduce the vulnerability to nuisance tripping: phase detection to eliminate sensitivity to capacitive leakage and a more elaborate two-stage time delay to reduce vulnerability to transients. Results obtained with a prototype design are presented to confirm the improvement in performance