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PME vs TT for charger

garywwess
Can someone please explain in common scence English (this has to be explained to a customer) ..  why it is permissible for a street light , which in itself is basically a big metal earth rod buried 5 feet in the ground.. is allowed to be PME`d  (customer used to install street lights) yet his charger has to be TT`d  and isolated from the PME at all costs..  his parking space has a street lamp smack in the middle of it ???  I neither agree or disagree with the instructions to do so… just need something in writing to show the customer to prove im not just generating extra income needlessly..

Gary
 
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    Chris Pearson:

    Concerning separation of different earthing systems: is it permissible to place an earth rod close to the DNO's service cable? I cannot see how they would interfere with each other except in the event of damage to the latter.




    If the service cable is sheathed, the only problem you might think you have is striking the buried service ... not always possible to accurately locate them.


    However, surge protection (and likewise EMC) might be an issue. If you have premises where surge protection is required (or specified), the TT electrode should be separated physically to avoid importing impulses from capacitive coupling in the same manner as not separating circuits. In this case, you're importing through the earth electrode, rather than the run of the cable.


    So, the answer is, it depends on the particular installation.

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    Chris Pearson:

    Concerning separation of different earthing systems: is it permissible to place an earth rod close to the DNO's service cable? I cannot see how they would interfere with each other except in the event of damage to the latter.




    If the service cable is sheathed, the only problem you might think you have is striking the buried service ... not always possible to accurately locate them.


    However, surge protection (and likewise EMC) might be an issue. If you have premises where surge protection is required (or specified), the TT electrode should be separated physically to avoid importing impulses from capacitive coupling in the same manner as not separating circuits. In this case, you're importing through the earth electrode, rather than the run of the cable.


    So, the answer is, it depends on the particular installation.

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