Earth-leakage protection in parallel with a solid earth

摘要

The trip coil of a voltage-operated earth-leakage circuit-breaker is likely in practice to be paralleled by a ????????solid???????? earth by reason of contact between the frame of the protected apparatus and fortuitously earthed metal. Itis better to provide a parallel solid earth of known performance. In such a protective circuit the sensitivity of the voltage-operated trip of the circuit-breaker may be increased without fear of unwanted operation due to leakage from apparatus such as anelectric cooker, and there are advantages over the more usual method of connection without a solid earth in parallel.