Earth electrode In rock

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Dan L
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Earth electrode In rock

Post by Dan L »

Location surrounded by volcanic rock.

Mains trench has been cut I to rock them will be filled in.

As far as earth electrode options

- horizontal
- vertical
- rio/ foundation

Would all be Into rock

I hear its possible for network to supply an earth from pos in some cases.

In regards to the rules of location

5.3.6.4 Location
Earth electrodes shall be installed in a location that satisfies the following
conditions:
(a) The electrode maintains effective contact with moist soil that is not
subject to excessive drying out.
NOTE: This condition is deemed to be satisfied by locating the electrode—
(a) external to the building in ground that is exposed to the weather; or
(b) in other locations where the ground remains moist because of soil
conditions or covers that reduce loss of moisture..


I don't think rock is soil but I woukd of thought it would hold moisture and be path?


If the mains trench is filled with soil then can a burried earth be used in that trench seems to satisfy the rules

Of same for vertical if area around filled with soil.

Thoughts and suggestions please
AlecK
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Re: Earth electrode In rock

Post by AlecK »

Rock isn't soil; and most types don't retain moisture.

Horizontal electrodes are generally better than vertical.
And the back-filled trench will count as "soil'.
After all; you'll have put in some bedding for the cable even if most of the back-fill is stone.
So if you have a nice handy trench for the mains; use it to lay a horizontal electrode.

If using eg 25 mm2 Cu conductor; and not far between point of entry and MSB, don't bother joining on a separate MEC;
just continue the run directly to MSB (but without stripping the insulation off the conductor)
No join means no label required, but remember to provide access for testing close to entry.
(eg flush box & labelled blank plate)

--------
Using the foundation is acceptable provided the foundation is in direct contact with ground.
Many slab floors aren't, as they have a damp-proof (and insulating) layer, plus often thermal insulation as well.
Dan L
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Re: Earth electrode In rock

Post by Dan L »

If the foundation is only in contact with the Rock ground is that still OK?

Seems horizontal earth will be best option here either way?
AlecK
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Re: Earth electrode In rock

Post by AlecK »

Yes concrete foundation in direct contact with ground complies with Exception (b) to 5.3.6.2, even if the "ground" happens to be rock .
And yes a horizontal electrode is likely to be superior.

Bearing in mind that you may need to bond the floor slab anyway, for other reasons [5.6.2.5]
Dan L
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Re: Earth electrode In rock

Post by Dan L »

Thanks mate much appreciated
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