What type of earth is this?

[ProDave]

I'm wiring a new build out in the country, and the supply was installed today.

It's served with it's own individual transformer on a pole from a SP 10KV line.

I asked the DNO guys first thing will it be PME but they said no as it's a single dwelling then described it in terms I have never heard before and can't now remember. (why can't they use the same descriptions as 7671 when describing earthing arrangements)

Anyway I remember they said they were burying an LV earth wire in a trench in one direction, and a separate HV earth in a trench the other way from the pole (I presume that one is to earth the transformer)

I left the site to do another job and when I got back the supply was connected so I didn't get to see how many cores in the incomer, but I don't think the earth they provided comes from neutral in the cut out. Ze measures 0.6 ohm so clearly earth connects to neutral somewhere, probably at the transformer.

So my guess is it's a TN-S, would you agree?

If so do I need to supplement the earth with a local earth rod, or just rely on the earth supplied by the DNO?

 

[Lurch]

If you ask them they will tell you what the earth type is, if they start waffling on they still know what TN-S etc... are, or ring up and ask them, the answer the office jockey gives will generally be less technical.

 

[Andy™]

TNS can be 0.8 ohms. no need to add another rod

phone call to DNO should get you your answer on to if it is TNS or TNCS (id hope TNS by the reading though!)