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tank/hv earth electrode and nearby concrete pad with mounted lighting column

psychicwarrior
Hello - good day to all !


Any experience/experiences that might provide a few tips/watch out fors etc, most gratefully received.


Contemplating the run of buried SWA cabled over 100m for outdoor lighting (and electric gates) passing by a pole mounted transformer, where it's been confirmed by the distributor that there is a Tank/HV earth electrode setup  at the pole. Whilst explaining this was not a rigid rule (more a guide and just as well as it shuts off the only feasible route), it was suggested best [in this case] to stay out of a 9m radius if burying cables - but the situation would be helped if this had to be compromised, by running the cabling in ducting/conduit when in the ground.


What are opinions on the siting of concrete pads with threaded rod to secure [conductive] column lighting in this context; this would seem a more serious concern within the 9m advice, is it a no-no, is there anything that can be done to mitigate (aside to using all non-conducting materials), or is it a non-issue (I feel not) ? 


I have no experience of such a long distance, but any tips and advice on pulling SWA along duct for over 100m would be uiseful too :-)   \\m/


Thank you all

Habs

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    ebee:

    So if we have a number of lamposts in a field we could have :-

    1/ Each lampost is it`s own TT electrode    or

    2/ As in 1/ above but  all linked (from 1st to last) by a common cpc.


    I`d instantly envisage the benefits of 2/ being a lower ohmic connection to "true earth" but what are the de-merits?


    As I see it the problem is that the ground in different areas can be a significantly different potentials (especially during a HV fault) - near to the Tx (and so near the HV electrode) it might be thousands of volts above normal, a few metres away it might only be a few hundred, a few tens of metres it'll likely be more pretty much zero. Stood at any one point the voltage difference should be small (foot to foot or foot to hand on something metallic stuck into the ground right next to where you're standing) - but anything metallic spanning across those different areas risks exposing someone to a very large difference in voltage.


    Hence the suggestion for a separate little TT island for each item.


    I suppose another approach in theory would be a Class II approach - so no exposed-conductive-parts and the metallic column etc not bonded (but could be in contact with the soil) - but the UK's phobia about relying on double/reinforced insulation (e.g. 412.1.2) makes that approach tricky, especially for domestics.


      - Andy.


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  • 0
    ebee:

    So if we have a number of lamposts in a field we could have :-

    1/ Each lampost is it`s own TT electrode    or

    2/ As in 1/ above but  all linked (from 1st to last) by a common cpc.


    I`d instantly envisage the benefits of 2/ being a lower ohmic connection to "true earth" but what are the de-merits?


    As I see it the problem is that the ground in different areas can be a significantly different potentials (especially during a HV fault) - near to the Tx (and so near the HV electrode) it might be thousands of volts above normal, a few metres away it might only be a few hundred, a few tens of metres it'll likely be more pretty much zero. Stood at any one point the voltage difference should be small (foot to foot or foot to hand on something metallic stuck into the ground right next to where you're standing) - but anything metallic spanning across those different areas risks exposing someone to a very large difference in voltage.


    Hence the suggestion for a separate little TT island for each item.


    I suppose another approach in theory would be a Class II approach - so no exposed-conductive-parts and the metallic column etc not bonded (but could be in contact with the soil) - but the UK's phobia about relying on double/reinforced insulation (e.g. 412.1.2) makes that approach tricky, especially for domestics.


      - Andy.


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