There is an article in PE and I have just received it via email.
I am disappointed that the article seems to suggest that it contains all you need to know yet no mention is made of earthing systems
AJJewsbury:
I might be talking out of my hat here, but why not combine both systems? Why not export PME via the swa and 3rd core, tie both together at both ends, the tie both to a rod at the destination end too? Belt & braces?
That would still suffer all the disadvantages of PME earthing. Unless the rod had a ridiculously low resistance to Earth (<< 1 Ohm) you'd still risk a hazardous potential on the earthing system during an open PEN event and the rise in potential of the soil around the rod would likely be far too steep to provide anything like equipotentiality in the vicinity of the tub. A buried grid under the entire area would probably be the minimum if you were going for that sort of approach.
- Andy.
Andy,
How does the 1 ohm that align with the NOTE in 702.410.3.4.3, which says 20 ohms, and only a "mat or electrode' - not a grid? I do accept that there's a difference between BS 7671 and G12/4 in that the latter discussed a buried grid under zone 2 (implying exactly what you're saying), but that does not give earth electrode resistances … so would I still refer back to BS 7671 for that?
AJJewsbury:
I might be talking out of my hat here, but why not combine both systems? Why not export PME via the swa and 3rd core, tie both together at both ends, the tie both to a rod at the destination end too? Belt & braces?
That would still suffer all the disadvantages of PME earthing. Unless the rod had a ridiculously low resistance to Earth (<< 1 Ohm) you'd still risk a hazardous potential on the earthing system during an open PEN event and the rise in potential of the soil around the rod would likely be far too steep to provide anything like equipotentiality in the vicinity of the tub. A buried grid under the entire area would probably be the minimum if you were going for that sort of approach.
- Andy.
Andy,
How does the 1 ohm that align with the NOTE in 702.410.3.4.3, which says 20 ohms, and only a "mat or electrode' - not a grid? I do accept that there's a difference between BS 7671 and G12/4 in that the latter discussed a buried grid under zone 2 (implying exactly what you're saying), but that does not give earth electrode resistances … so would I still refer back to BS 7671 for that?
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