| 摘要 |
<p>A residual current operated device comprising means for sensing an imbalance between the currents flowing in the line and neutral conductors (12, 14) connected by way of connecting switch (22) between an a.c. source (18) and a load (20). A control circuit having an input coupled to the sensing means and arranged to provide a control signal to open said connecting means (22) if the magnitude of said imbalance exceeds a predetermined value. The sensing means comprises a current transformer (24) having a sense winding (26) for providing an output signal dependent upon the imbalance of the currents flowing in the line and neutral conductors which pass through the current transformer. A detector circuit is provided for detecting an open circuit in the sense winding circuit and for opening said connecting switch in consequence thereof. The detector comprises means (80, 52, 32, 34) for generating a potential difference across the sense winding. A comparator (46) detects a change in the magnitude of said potential difference from a first level when the sense winding is continuous to a second level if the sense winding is open circuit and is arranged to open the switch (22).</p> |
