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PME vs TN-C-S

AncientMariner
Are PME and TN-C-S supplies exactly the same?  Or does PME also have requirements regarding the number and relative location of suppliers earthing rods?

I am thinking here where the DNO replaces a length of failed 4-core (3-phase + Neutral) PILC cable with Wavecon or similar cable which has a combined Neutral and Earth conductor.  The average consumer would not know that their electricity supply's method of earthing had been changed.

Clive.
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    PNB is also (most of the time) PME in a public distribution network,

    If it helps understanding at all (or just reduces the opacity of the soil water emulsion slightly), my head distinguishes between PNB being PME and PNB should be treated as if it might be PME.


    In my head, PNB clearly can never be PME - any system has a certain number of points where the N is deliberately earthed - if it's one it cannot be PME, if it's greater than one it cannot be PNB. The definitions do not overlap.


    On the other had we have the problem of DNOs changing things - what was PNB one day might be converted into PME the next - or indeed what was originally a pure TN-S system being converted into PME - usually entirely unbeknown to the consumer, The lead sheath earth at home is as likely to be PME as TN-S (probably more than likely these days) - most of the time we simply can't tell. So the advise is to treat any DNO earth facility as the worst case - i.e. as if it were (or could soon become) PME. You might think of this as being where "PME conditions apply" rather than the earth terminal actually being PME,


       - Andy.
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  • 0
    PNB is also (most of the time) PME in a public distribution network,

    If it helps understanding at all (or just reduces the opacity of the soil water emulsion slightly), my head distinguishes between PNB being PME and PNB should be treated as if it might be PME.


    In my head, PNB clearly can never be PME - any system has a certain number of points where the N is deliberately earthed - if it's one it cannot be PME, if it's greater than one it cannot be PNB. The definitions do not overlap.


    On the other had we have the problem of DNOs changing things - what was PNB one day might be converted into PME the next - or indeed what was originally a pure TN-S system being converted into PME - usually entirely unbeknown to the consumer, The lead sheath earth at home is as likely to be PME as TN-S (probably more than likely these days) - most of the time we simply can't tell. So the advise is to treat any DNO earth facility as the worst case - i.e. as if it were (or could soon become) PME. You might think of this as being where "PME conditions apply" rather than the earth terminal actually being PME,


       - Andy.
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