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Can you confirm type of earthing


roys

Question

Morning Folks

Friend asked me a couple of questions about his place, so property is remote has it's own tranny on a pole outside, I can see the phase and neutral leaving the pole and going into the ground, I can also see an earth cable leaving the case earthing bolt on the tranny and going into the ground. At the house I can see the cable coming in and an earth coming in. I am guessing the earth coming in is the earth from the tranny casing. I that a fair guess? There is a 30mA RCD seperate to the CU, do you think Scot Power fitted this? When I initially saw the RCD I thought it was a TT system but when I looked a little closer at the connections I think it is TVC-S, as the neutral and earth are connected together before the meter, can you confirm or enlighten me. Please see attached images (I hope).

Also and the question I am dreading asking is, he wants to supply a garage 30meters from the house, can he export the earth (aahhhh sorry) or is it a case of terminating the SWA into a plactic JB and then out on 2 tails to the garage CU and earth spike the garage. Garage is block construction with no water or gas pipes going into it.

Thanks in advance Steve

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16 answers to this question

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Looks like TT converted to TNC-s. Think I would treat system as TT - bum covered in all directions including exporting earth (rod the garage)

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green-hornet

To be fair it does not look like a job the dno would do, the concentric cable would have been properly sheathed or compression taped before connection to the nuetral block.

The plot thickens.

I would be interested in the outcome of this mystery, please let us know what you find out.

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Couple of observations not all relevant, but whats with T&E going all randomly upwards toward the CU and why are the nails not banged in fully on the clips.

Last and no means least who nicked the cover for the concentric incomer, or did it get removed so the 2 gang switch could fit in.

Hi Ian932

It was me who flicked the cover for the sake of the photo, (mentioned it in an earlier post), put the cover on after pic was taken. 2 gang switch is not in the way.

The T&E were flapping in the wind, think he just tacked them back.

Cheers Steve

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All transformers will be earthed that is how they get there neutral connection. Looks like pme to me, what is earth fault loop like if its less than

.35ohms generally dno will give pme earth. You can always TT it if you want and not use the pme earth. I did this recently on a job as supply originally was a distance from building. When meter was moved to house I left rod in as I did not want to test all the electrics again. I personally would TT outbuilding because thats the way I do it. But you could do it by taking TT earth from house if you wanted.

Batty

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Bit of a bump (since Steps and Ian are having some sport over earthing :)) and an update.

So I was talking to mate at the weekend on the phone, he told the electricity board was up working near by, so he got them over to give them the 3rd degree. So one of the board guys said 'I remeber doing this about 6 or 7 years ago, he said that the earth leaving the transformer, so goes to a bit of bare 70mm copper cable in the ground to earth the tranny.

The earth leaving the house terminates onto a bit of bare 35mm copper cable which he said ran in the cable trench for a couple of yards.

Not been back to his place so unable to check Ze.

Does this change anyones opinion?

Still TNC-S?

Don't export earth to garage?

Cheers Steve.

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green-hornet

I can be 100% sure it is a pme.

If you look at the earthing/nuetral block you can see the neutral leaving the same block to the meter.

The earth you see from the box outside is the local earthing only for that box.

I would TT the garage saves a load of hassle, well to me anyway.

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ianmacd

It looks like PME supply presented as TN-C-S with a earth electrode on the incomming PEN. This does support the argument that DNO should be putting in electrodes on a PME network. I wish this was more common with TN-C-S.

Yes, would still TT the outbuilding and use the earth from the supply on the armour and isolate at the outbuilding's Earth.

Thanks for bumping this back up for our attention.

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I can be 100% sure it is a pme.

If you look at the earthing/nuetral block you can see the neutral leaving the same block to the meter.

The earth you see from the box outside is the local earthing only for that box.

I would TT the garage saves a load of hassle, well to me anyway.

I agree it looks like PME, but as the cover is off/missing and not sealed anyone could have put that earth in ? Unfortunately the suppliers use any odd connector they have to hand. As mentioned above test the Ze and compare that to the maximums allowed. It does not look like there is a PME sticker. The official answer would be to call the supplier ROTFWLROTFWLROTFWL

PS, Was the cable cover missing ?

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Evans Electric

Must admit ,I'm confused, which is nothing new, but I see a split concentric cable with an earth coming off the neutral block so you'd think , TNC-S but that incoming earth cable is confusing me . The tranny looks like 400v 2 phases to single phase 240v with a neutral/earth point centre tapped.

Perhaps Sparkss the e-on jointer can help.

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Couple of observations not all relevant, but whats with T&E going all randomly upwards toward the CU and why are the nails not banged in fully on the clips.

Last and no means least who nicked the cover for the concentric incomer, or did it get removed so the 2 gang switch could fit in.

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PBC_1966

Definitely PME supply and TN-C-S by the descriptions then.

The tranny looks like 400v 2 phases to single phase 240v with a neutral/earth point centre tapped.

Not sure what you think you're seeing there. Looks like a pretty common single-phase transformer with 11kV (probably) primary and 240V secondary to me.

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mmm the plot thickens indeed.

Ask the DNO, wonder if they will know?

But are we all agreed, don't export the earth to outbuilding, and earth rod the outbuilding instead?

Cheers Steve

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SPECIAL LOCATION

Is that a VOELB (Voltage-Operated earth-leakage circuit breaker) on the second photo?

which points toward it being a TT at some stage in the past...

But the the income cable to me says (100% al-la Green Hornet) PME, (TN-C-S)

is the earth wire going down definitely coming into the installation?,

or could it be a bonding conductor off to some water/gas pipework?

:|?:|

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mmm the plot thickens indeed.

Ask the DNO, wonder if they will know?

But are we all agreed, don't export the earth to outbuilding, and earth rod the outbuilding instead?

Cheers Steve

yes :) -

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Thanks all so far.

To answer some of the points raised so far.

The cover is missing on the earth neutral connector cos I flicked it off for the pic, clicked back on now, but it is not tamper proof.

The main earth coming in confuses me, it does not go to a gas pipe as there is no gas, the water pipe coming in is a 25mm plastic pipe from the properties own well and I would doubt it comes from that. Fairly convinced it is a DNO supplied earth but from where I don't know. Didn't have any kit with me as I was only down there for a beer so have no earth loop test readings.

No PME stickers anywhere to be seen.

I agree the connector block connection points to PME, but it is strange.

Cheers Steve

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