| 摘要 |
<p>An apparatus is provided for monitoring the earthing of an installation which receives alternating supply current of a first frequency and which is provided with earth leakage protection. Injecting means (12, 28, 29, 30) injects alternating current of a second frequency into an earthing conductor and measuring means (13, 31, 32, 33) measures the resulting current flowing through the conductor so as to provide a measure of earth impedance. The earth leakage protection is insensitive to current of the second frequency. When the earth impednance is too high for proper operation of the arth leakage protection, a warning indication is given.</p> |
