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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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    Chris Pearson:

    This subject popped into my head again just now.


    Current situation: supply to single premises branches off close to the transformer, perhaps where the LV side of the transformer is earthed. (I have not looked closely.)


    Assuming that the PSSC, and thence the PEFC could be brought below 0.35 Ω, where and how do you plant the extra earths which will make it PME?


    If your consumer's supply "branches off" then presumably there's a "main" continuing off to serve other consumers. If so I think the minimum requirement for PME is to have an additional electrode connected to the CNE at the point where the last consumer branches off from the main.

      - Andy.


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  • 0
    Chris Pearson:

    This subject popped into my head again just now.


    Current situation: supply to single premises branches off close to the transformer, perhaps where the LV side of the transformer is earthed. (I have not looked closely.)


    Assuming that the PSSC, and thence the PEFC could be brought below 0.35 Ω, where and how do you plant the extra earths which will make it PME?


    If your consumer's supply "branches off" then presumably there's a "main" continuing off to serve other consumers. If so I think the minimum requirement for PME is to have an additional electrode connected to the CNE at the point where the last consumer branches off from the main.

      - Andy.


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