Q & A of the Day - Earth fault loop impedance testing

Question: Could you please tell me if whether could carry out earth loop impedance testing (ie: Ze and Zs) if there is no equipotential earth bonding connected. When using a Meggar LT7 digital loop tester, it appears that the instrument goes through a checking process before the test is displayed.

Answer: I'll discuss the checking process in a moment. First, when measuring Ze, the means of earthing must be disconnected from the installation earthed equipotential bonding for the duration of the test to remove parallel paths.

When measuring Zs, neither the means of earthing, nor the bonding conductors, must be disconnected to retain the parallel paths. The Megger LT7 carries out an initial low current check to calculate what the contact voltage on accessible metalwork will be in a real fault. It must be less than 50V for the test to proceed.

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