| 摘要 |
<p>This invention relates to a method and apparatus for monitoring the earth loop impedance of an electrical installation that is protected by a circuit protection device, such as a residual current device. The method and apparatus enabling an earth loop impedance test to be performed on an electrical installation without tripping the circuit protection device. In use, the present invention is achieved using an earth loop impedance tester that automatically signals to any circuit protection devices present in the electrical installation that an earth loop impedance test is about to be performed. The circuit protection device can detect the earth loop impedance tester's signal sequence which comprises a first part of the sequence to disable operation of the circuit protection device for a predetermined interval and a second part of the sequence to monitor the earth loop impedance of the electrical installation. The second part of the sequence, which monitors the earth loop impedance of the electrical installation, is representative of the normal supply frequency of 50Hz or 60Hz. After this predetermined interval during which an earth loop impedance test has been performed, the circuit protection device reverts back to its normal mode of operation.</p> |
