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my surge protection 'cpd', such as it is...

psychicwarrior
Good morning all


I have obtained the following [I feel as the] 'best we can do for now' information from the DNO. They were helpful in my test case request for info.


"...address 1:

LV underground - 362m

HV underground to primary-  2000m

No Surge protection devices


address 2:

LV underground to substation - 110 m

HV UG from substation to HV pole is 823m then 301m 11kV overhead then 190m HV UG to the primary substation.

Distance to cable termination with surge protection device from secondary substation is 1124m (823m 11kV UG + 301m 11kV Overhead).  The nearest cable

termination does not have surge protection installed. ..."


In relation to the risk assessment equation variables dealing with distribution cable lengths  ie. the Lpal Lpcl Lpah Lpch, how would one fit the given values into the variables ?


For addr1, ignore the HV (e.g. use zero for Lpah Lpch),  then take Lpcl as 362 and Lpal as 638 ?


For addr2, i'm not sure on this one ?


Thanks for your input.

Habs


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    Alasdair Anderson:

    Better - the optimum path for the lightning strike is now your neighbour's aerial......

    A long time since I did this at university (or possibly earlier) but dredging my memory banks, the reason lightning conductors are sharp spikes is that the radius of the tip (i.e. how sharp it is) affects the ionisation potential and so makes it a more attractive conductor for lightning. If there is a roof in the way it should make a big difference, particularly if it is raining and the roof is wet, a high probability in a thunderstorm. Of course if your house is on a hill and you have no neighbours it may still make your house the most likely point to be struck.




    This is true, but perhaps a little irrelevant to BS 7671.


    BS 7671 doesn't cover direct strokes [not a spelling mistake], so I guess we are really looking at induced or capacitively-coupled voltages. From this perspective, there's probably a slight advantage over external roof-mounted, but perhaps not much dependent on what the roof materials are?

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  • 0

    Alasdair Anderson:

    Better - the optimum path for the lightning strike is now your neighbour's aerial......

    A long time since I did this at university (or possibly earlier) but dredging my memory banks, the reason lightning conductors are sharp spikes is that the radius of the tip (i.e. how sharp it is) affects the ionisation potential and so makes it a more attractive conductor for lightning. If there is a roof in the way it should make a big difference, particularly if it is raining and the roof is wet, a high probability in a thunderstorm. Of course if your house is on a hill and you have no neighbours it may still make your house the most likely point to be struck.




    This is true, but perhaps a little irrelevant to BS 7671.


    BS 7671 doesn't cover direct strokes [not a spelling mistake], so I guess we are really looking at induced or capacitively-coupled voltages. From this perspective, there's probably a slight advantage over external roof-mounted, but perhaps not much dependent on what the roof materials are?

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