| 摘要 |
A circuit for supplying electric current comprises phase, neutral and earth conductors and a residual current conductor for conducting to earth intentional residual currents from filters and the like. A residual current circuit-breaker disconnects at least the phase conductor when the vector sum of currents in the phase, neutral and residual current conductors indicating a leak to earth exceeds a given magnitude. A switch may be provided to connect the residual current and earth conductors when the current in the residual current conductor exceeds a given value and the residual current conductor may have an impedance so that leadkage passes through the earth conductor if it is short-circuited to the residual current conductor.
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