21 Apr 2012
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United Kingdom
Currently getting quotes to upgrade our old fusebox to a 10/12 way RCBO consumer unit.
Getting different advice regarding some earth issues, and wanted to check.

With the earth bonding inside our house we have three earth wires from the bathroom, that go into a earth connector block, one cable then goes into another earth connector block where it joins the gas main earth, and goes back to the CU. One electrician said using exposed earth connector blocks is a big no no, and is looking at re pulling cables for continuous runs, the other saw no problem.

Currently we are supplied with overhead cables, we have a earth spike so assume using TT - the earth spike is uncovered and is slightly corroded. One electrician said he would replace & cover. The other didn't seem concerned (no requirement for it to be covered) and said it would be much better to get PME from the DNO anyway.

Incidentally the DNO has a PME earthing box on our house.
Does either option TT/PME make more sense?
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PME would be my preferred option.

Some DNO's will not provide PME if the service drop the house is two single core cables (as in the ones in your pic). It maybe PME upto that joint on the wall, but whether they will give you a PME connection is upto them. Certainly worth asking - They may replace your service cable drop from that joint box to your service head as a matter of course.

You should have a 10mm earth cable from the gas and water in a continuous run (any joints crimped). If this 'exposed' terminal you speak of is at the origin / close to the CU, there is no issue. It would essentially be your MET, and it being exposed is not an issue at all.

Rods should be protected from damage - If it is not prone to damage due to it's location, a cover or pit is not required.

Regarding your 10/12 way RCBO CU - I used to prefer to use RCBO's, but these days am more than happy to fit a Dual Split load board. While RCBO's do mean less interuption when a circuit trips, you do not know if they have tripped due to overload or earth fault. This can be useful to know, even in the presence of a test instrument and the knowledge of how to use it.
The label on the box should signify that the neutral is bonded to the cable shesth at the box, the earth wire coming out seems to confirm this. That being the case all supplies fed from that box will already be PME, though they may not be connected in the properties (which seems to be the case)

Yes you need to talk to the DNO
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Yeah, maybe PME outside, or even inside at the service head, but does not mean it is a PME installation within the property.

MEB in Staffs are good at this: They PME all the cutouts on the old TT supplies. But they only ever reinstate TT inside the house as that was what was there before they arrived....When I talked to an MEB guy he said they didn't want to take responsibility for having PME in a property where there may be no PEB's.

Never mind a TT install with no RCD's... ;)
Generally we will leave the earthing arrangement as we find it unless we have specific contact with someone who can ensure that bonding is correct.

The problem arises if they are not up to a modern spec, we have two choices leave it as found or declare it dangerous and disconnect it. If we chose the latter there would be a lot of folk without a supply!!
Yes you need to talk to the DNO

Thanks, DNO is fully booked at the moment, so have to call them back in June to book an engineer visit.
They said all they will do is test whether PME is available, they won't 'supply' the earth and that is up to the sparkie. Is that correct - I thought an electrician wasn't allowed to add the earth to the cutout?

They will test the earth loop, and I would expect they will then add a henley block connected to the neutral ready for your electrician to connect to.

Looking at your service head, you have a concentric drop and not two seperate tails which is good - My DNO will not usually PME a supply with the two seperate tails, only with concentric drops.

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