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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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  • 0
    For what it's worth I too wouldn't be comfortable with a TT solution for equipment installed within the hot zone and supplied from an external LV source for the reasons that Alan and Andy set out. Also worth bearing in mind that we're not just talking about operators immediately in the vicinity of the hot zone: By installing conductors you may well create situations where the HV substation local earth potential is exported through the LV installation to others where precautions you might consider reasonable around a lampposst (e.g. shoes) aren't being taken. In other words you might be extending the substation hot zone into the house at the far end of the LV cable...


    For substations where the auxiliary LV supply is derived from an external LV source (e.g. 33kV sub fed from local network for resilience), it would be normal to feed the equipment via an isolation transformer, with a locally arranged TN earth.


    To put it into context Openreach require the installation of isolation transfomers at each end of each cable where a new substation imposes a hot zone that crosses their existing telecoms network, because of the risk to their remote equipment (and personnel).


    I would suggest, if possible:

    a) Confirm with the DNO whether the substastion really is hot, and if so where the hot zone contour actually is and what their rules are

    b) Re-route to avoid the hot zone

    c) Install cables within suitably insulating ducts and derive any equipment within the hot zone from an isolation transformer (rated for the EPR of course)


    Lastly do be careful if you're digging a trench across the hot zone as you might well expose - or worse damage - the electrode, especially if it's laid horizontal, which could well present a hazard to site operators.

     
    mapj1:

    Or  for light duty situations  the all-insulated lamp post  You could do worse than call them to see what they offer for your situation Tel +44 (0)1623 511 111  I have no connection with the company other than our maintenance folk ordered a replacement post for a funny situation from them once.


    Hmm, interesting, one for the potentially useful products library, thanks!


Reply
  • 0
    For what it's worth I too wouldn't be comfortable with a TT solution for equipment installed within the hot zone and supplied from an external LV source for the reasons that Alan and Andy set out. Also worth bearing in mind that we're not just talking about operators immediately in the vicinity of the hot zone: By installing conductors you may well create situations where the HV substation local earth potential is exported through the LV installation to others where precautions you might consider reasonable around a lampposst (e.g. shoes) aren't being taken. In other words you might be extending the substation hot zone into the house at the far end of the LV cable...


    For substations where the auxiliary LV supply is derived from an external LV source (e.g. 33kV sub fed from local network for resilience), it would be normal to feed the equipment via an isolation transformer, with a locally arranged TN earth.


    To put it into context Openreach require the installation of isolation transfomers at each end of each cable where a new substation imposes a hot zone that crosses their existing telecoms network, because of the risk to their remote equipment (and personnel).


    I would suggest, if possible:

    a) Confirm with the DNO whether the substastion really is hot, and if so where the hot zone contour actually is and what their rules are

    b) Re-route to avoid the hot zone

    c) Install cables within suitably insulating ducts and derive any equipment within the hot zone from an isolation transformer (rated for the EPR of course)


    Lastly do be careful if you're digging a trench across the hot zone as you might well expose - or worse damage - the electrode, especially if it's laid horizontal, which could well present a hazard to site operators.

     
    mapj1:

    Or  for light duty situations  the all-insulated lamp post  You could do worse than call them to see what they offer for your situation Tel +44 (0)1623 511 111  I have no connection with the company other than our maintenance folk ordered a replacement post for a funny situation from them once.


    Hmm, interesting, one for the potentially useful products library, thanks!


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