Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning the continuity of protective conductor test result being greater than the measured earth loop impedance test result, is answered by SELECT:
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| A schematic of a radial circuit. |
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Question: During the testing of a small power 16A radial circuit, protected by a Type C MCB, the continuity of protective conductor test result (R1+R2), was in excess of the measured earth loop impedance test result (Zs). Is there a technical reason for this, and would this test result be acceptable?
Answer: The possibilities include problems with continuity or earth fault loop test instrument accuracy. Alternatively, the use of no trip test setting on some earth fault loop impedance testers {not always as accurate} only passes 15mA instead of 20-25A test current.
You do not mention whether any RCD protection of the circuit is in place. The Zs measurement and R1+R2 measurement may also be lower if measurement is carried out with other parallel connections to earth in place during test, i.e. main protective conductors connected/SWA connected and used in addition to the CPC of cable / metal conduit connected during testing of conductors / flying tails to back boxes/ etc…You do not specify the wiring type or method of installation either. Knowing this would help.
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