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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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Z.
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    Mind you over 300yds I'd expect them to have fitted something quite a bit heavier than 35mm wavecon. The neutral rise relative to terra-firma on full load (thinking about half of 0.48 ohms and perhaps 40A for an electric shower and a few lights ) must be quite noticeable! Or maybe the water pipes are taking quite  lot of neutral current, and the loop impedance of the main itself is really higher.

    There is a reason for the one metre one volt rule of thumb for planning networks - 230/400 V supplies become problematic in this way at the few hundred metres sort of range.

    Mike.
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  • 0
    Mind you over 300yds I'd expect them to have fitted something quite a bit heavier than 35mm wavecon. The neutral rise relative to terra-firma on full load (thinking about half of 0.48 ohms and perhaps 40A for an electric shower and a few lights ) must be quite noticeable! Or maybe the water pipes are taking quite  lot of neutral current, and the loop impedance of the main itself is really higher.

    There is a reason for the one metre one volt rule of thumb for planning networks - 230/400 V supplies become problematic in this way at the few hundred metres sort of range.

    Mike.
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