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VOLTAGE BETWEEN THE GENERAL MASS OF EARTH AND A PME NEUTRAL/EARTH

John Peckham
Other than under fault conditions or a small difference due to volt drop on a heavily loaded CNE cable can anyone explain why you may get a large potential difference (say 70V) between the general mass of earth and the MET on a an installation with a PME earthing system?


I have not seen this myself. If this does occur how rare or frequent might this circumstance occur?


If this potential difference does occur what sort of duration might this persist for?


Although a DNO may switch occasionally the HV ring for fault or maintenance works transformer neutrals remain bolted to earth and if the HV/LV earths are combined then an earth resistance of sub 1 ohm (in UKPN land that is what they want) so how can the neutral voltage float up more than a couple of volts above the general mass of earth?
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    A note on the John Ward video. The overload device on the E.60 V.O.E.L.C.B. did not appear to work correctly. It probably did not operate correctly with the cover of the device removed, as the operating lever overshoots and is not in the correct position when the O/L device is pressed. With the device's cover replaced I am sure that the O/L mechanism will operate correctly and switch off the main switch via the lever.


    Z..
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  • 0
    A note on the John Ward video. The overload device on the E.60 V.O.E.L.C.B. did not appear to work correctly. It probably did not operate correctly with the cover of the device removed, as the operating lever overshoots and is not in the correct position when the O/L device is pressed. With the device's cover replaced I am sure that the O/L mechanism will operate correctly and switch off the main switch via the lever.


    Z..
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