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TT to TN-C-S

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I advised a customer to have a new P.M.E. earth terminal installed by U.K.P.N. This was done. When U.K.P.N. attended and tested, the men found a weakness/imperfection/fault at the top of the nearest pole. A repair was carried out.


In my area many premises have old T.T. earthing. As a mater of course I would recommend that all T.T. premises be converted to TN-C-S where permissible, to improve the safety of the installation. 


Today I visited a house under renovation. The earthing conductor to an earth rod had been disconnected in the garden. The whole house was very dangerous due to an old and unearthed installation. The old Voltage operated earth leakage circuit breakers were unreliable. I disconnected many circuits.


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    Zoomup:
    Chris Pearson:
    Zoomup:
    Chris Pearson:

    I expect that there may be a range of opinions on this one!


    In any event, the premises must be sufficiently close to the transformer and the DNO must be willing.


    I have never had a refusal by U.K.P.N. to install a new P.M.E. earth terminal yet Chris. We have been treated to new A.B.C. over head cables out here in the sticks. And don't we need them with the strong winds coming off the North Sea!




    Best PSSC that I have recorded at Daughter's house was 0.480 kA. So that's a best case of Ze = 0.48 Ω and no chance of PME there. (Nice shiny new ABC too.)




    Perhaps down the line they need to get the wire brush and metal polish out at pole tops. Does your daughter live off planet Chris?




    It's just that the distance from the transformer to the cutout is about 300 yards, so 25 mm² (copper equivalent) conductors will never get to 0.35 Ω or below.


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  • 0
    Zoomup:
    Chris Pearson:
    Zoomup:
    Chris Pearson:

    I expect that there may be a range of opinions on this one!


    In any event, the premises must be sufficiently close to the transformer and the DNO must be willing.


    I have never had a refusal by U.K.P.N. to install a new P.M.E. earth terminal yet Chris. We have been treated to new A.B.C. over head cables out here in the sticks. And don't we need them with the strong winds coming off the North Sea!




    Best PSSC that I have recorded at Daughter's house was 0.480 kA. So that's a best case of Ze = 0.48 Ω and no chance of PME there. (Nice shiny new ABC too.)




    Perhaps down the line they need to get the wire brush and metal polish out at pole tops. Does your daughter live off planet Chris?




    It's just that the distance from the transformer to the cutout is about 300 yards, so 25 mm² (copper equivalent) conductors will never get to 0.35 Ω or below.


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