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Lightning electrodes

lyledunn

A relatively small parish church has 8 down conductors connected to rod electrodes. Each electrode measured separately ranged from 215 ohms to 12 ohms with the overall value being around 8 ohms. Now I am aware that the overall value should be less than 10 and that each individual electrode should be no more than 8x10. We have one at 215 and one at 135, the others meeting that requirement. It is easy for me to advise that the system does not meet code but I do not have the expertise to assess the implications of the situation. I would appreciate your opinion. 

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    The idea of lightning conductors is being misunderstood. Whilst a direct strike is possible, it is very unusual. The purpose is to reduce the electric field above the building, which is why the electrodes on high points have sharp “points”, and therefore reduce to chance of a nearby discharge. Direct hits on most systems will produce damage to some level. Many kA will pass along the conductors and the potential will be dangerous whatever one does. Ohms law of several kA and 10 Ohms is? It is unlikely that the electrode resistance will make all that much difference, at these voltage and current levels the electrode resistance is highly non-linear anyway. The COP is as usual a guide to new systems, as most of you realise, getting a 10 Ohm Earth is difficult at the best of times, and the electrodes may well need to be multiple and long! Modern systems tend to use the foundation concrete, but this will not be present in an old building. 

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    The idea of lightning conductors is being misunderstood. Whilst a direct strike is possible, it is very unusual. The purpose is to reduce the electric field above the building, which is why the electrodes on high points have sharp “points”, and therefore reduce to chance of a nearby discharge. Direct hits on most systems will produce damage to some level. Many kA will pass along the conductors and the potential will be dangerous whatever one does. Ohms law of several kA and 10 Ohms is? It is unlikely that the electrode resistance will make all that much difference, at these voltage and current levels the electrode resistance is highly non-linear anyway. The COP is as usual a guide to new systems, as most of you realise, getting a 10 Ohm Earth is difficult at the best of times, and the electrodes may well need to be multiple and long! Modern systems tend to use the foundation concrete, but this will not be present in an old building. 

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