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Hi Guys，

New townhouses built on volcanic rock. There is no chance for Vertical earth electrode. Can only try Hotizontal eletrode, normally, 7.5m long naked 25mm2 CU. The questions are:

1. is there any restriction on the shape of laid 7.5m naked 25mm2 Cu? I did not see any information in the reg. Giving the limited yard space of the townhouses, can we lay the 7.5m naked 25mm2 Cu like what we do for underfloor heating? Circles in circle or squares in square. I do not see any problems here as long as following the key pricinples: keep the earth electrode moist. the gap between the circles or squares should be as big as possible. But is there any minimum gap recommended in the reg or somewhere?

2. I have been told by the inspector that the nearby main earth electrode should be at least 1.5m apart from each other. But I cannot find in the reg. Can someone tell me where to find these information?

Thank you.

There is no rule on either shape or separation in "3000".
But clearly the straighter the better and the further apart the better.

In "3017", Fig 3.23 illustrates testing resistance of earth electrode;
and suggests 30 - 50 m separation between the electrode being tested and a second electrode used to test it;
to ensure that the "resistance areas' of the two electrodes don't overlap.

AlecK, I think you are missing the critical wording of the clause "... a minimum horizontal length of: .. (ii) In New Zealand, 7.5 m."

It's not going to have the minimum horizontal length if it's laid in a loop, or even a U shape.

That doesn't mean it has to be in a straight line. Eg could run for 3 m in one direction, then turn a corner for the rest.

It could go out for 2.5m across for 2 m, and back parallel for 2.5 m; gibing total length of 7.5 m and min separation of 2 m.
Not ideal, but we sometimes have to deal with restricted sites

And that's a minimum length; could be many meters ; though less likely these days.

The old ESA's had the power to reject a standard by-the-book electrode.
it was very common on my area (same as yours) to be required to add a second driven electrode if the inspector felt one wasn't good enough
I also recall one in the neighbouring area where each day the Inspector would turn up, decide it wasn't good enough, and we'd spend the rest of the day digging another there-&-back trench in the lawn. After a week the entire lawn looked like a large-scale in-floor hearing element had been laid, with the trench snaking back & forth in parallel lines. With VERY unhappy owner!
All because the network was using the installation electrodes to try to hod their distribution N down somewhere close to zero volts; and the ground was poor.

These days we only have to have one electrode that complies with the Standard. Networks have to find other ways of pulling n-voltage down when needed, not loading the cost onto installers working on quoted jobs.

After all the effectiveness of the installation electrode is not about the numbers for that particular installation; it's about the fact that multiple installation electrodesare all in parallel; with Ohm's Law ensuring that - overall - the impedance to mass of earth is low (that's MEN)

https://www.electrical-installation.org ... lectrodesk

This is a good reference, horizontal earthmats have many advantages as vertical earth's driven in poor conditions can record hundreds of ohms, plus if driven too close to each other will be less affective plus need separation from other earths where trenched earth's in moist soil conditions plus ground inhancing produces make them very effective.