Earthing question - TNC in Bulgaria - DIY

[ivantheterrible]

Hi all,

For clarity, I'm not a qualified electrician, but have a reasonable amount of experience as I've done plenty of wiring (signed off by a proper sparky) as a farm manager in the UK.
I now have a house in Bulgaria which we bought some five years ago and have been slowly modernising during any holidays. We have now moved over full time and I want to rewire as the wiring here is ancient and of very very dubious quality. Anyone who's seen old Bulgarian house wiring will know the sort of thing. Flat two core wire fixed with nails between cores, two or three china and wire fuses for the whole system and lights that piggy-backed off of the two pin sockets. The sockets themselves are either not earthed in some cases or share a joined negative / earth back to the fuse board. I originally put in a small CU to separate some of stand alone items such as the washing machine and cooker but had to follow the same combined earth neutral as most of the wire is two core. I now wish to put in a decent CU and new three core wiring throughout, making the system a TN-C-S one. I don't trust the old wiring as the house is 100+ years old and some of the wire is at probably 50 going by the old cloth style insulation tape used in many places. I'm worried that if one of the earth / neural cores break, items will become live, so it needs doing ASAP.

So, to my questions -
Starting at the meter box outside of the property, I'm not sure of the integrity of the earth system itself as there appears to be no earth rod at our post (we are a fair way from the transformer or other properties, so I would have expected one. To add to that, it looks like there should be an earth rod as the connection is there, but it goes nowhere - (see the pictures) Apparently, they sometimes going "missing". Would it be a sensible idea to install my own at this post or within my property, or would I risk creating an earth loop? Bear in mind our nearest neighbour is nearly a km away and the transformer even further. Of course, I could check with the supplier, but have so far found that asking them anything seems pretty fruitless.
Then, on the rewiring. I intend to stick with a radial circuit rather than ring, as I'm pretty sure that's against the reg's here. If so, can I combine both TN-C and TN-C-S on separate radials as I go along or will this cause issues? I intend to do the whole lot, but it may take a while, hence the combination until all is done.
Sorry, for the multiple questions, and thanks for any advice.

 

[pc1966]

I'm not sure who on this forum would know much about eastern European electrics, maybe @Lucien Nunes is the best bet.

Almost certainly an earth rod is a good idea, as is making it TN-C-S by separating out the N & E within the installation.

Since EU and rest of world sockets are unfused, the supply breaker has to be 16A, maybe 20A max, so there is no real point in making a ring circuit. That is done in the UK as a cost effective way of allowing a 32A supply for the sockets, thus increasing the number that is sensible to allow through greater diversity of loads (though we don't actually limit it), while keeping cable size and cost down and adding an element of CPC (earth) redundancy. But it depends on fused plugs as the UK (and a few other places) have to make sense.

 

[Rockingit]

I'm scheduled to be in Bulgaria in a couple of weeks (Sofia) - may/not have a few spare hours in the afternoon if so - is that of any use to you??

 

[ivantheterrible]

I'm scheduled to be in Bulgaria in a couple of weeks (Sofia) - may/not have a few spare hours in the afternoon if so - is that of any use to you??

Thanks for the offer but we're just about as far as it's possible to be from Sofia whilst still being in Bulgaria.

 

[Lucien Nunes]

The more of the neutrals and earths you can separate and the nearer the origin you can do so, the better. There's no harm doing that alongside existing combined neutral/earths so long as it is clear what's what.

Adding a rod makes sense, it's not going to have a low enough Ra to prevent all risk from touch voltage in the event of an open supply PEN but it's better than not having one.

TN-C is scary when unfamiliar but has been quite widespread and still recognised and used until recently in locations with high technical standards. A well-executed 1990s TN-C installation in Finland for example might not be quite so alarming as a Soviet-era one in BG. The devil is in the detail.

 

[Marvo]

I still come across TN-C installations living in Africa and even being familiar with the arrangement it still gives me the heebiejeebies.

If none of yor neighbours have TN-C-S / PME'd installations the danger of just you having one is that your earth rod could end up carrying large currents under certain supply fault conditions.

I'd suggest you might consider making it a TT installation (with RCD protection) by putting in a convincing earth rod, at least 4 or 5 meters deep and even 2 or 3 separate rods linked together with a wire the same size as your incoming supply or larger. Also if you've got a concrete slab with rebar or a steel outbuilding then connect to that as well. If you've got a bore hole with a steel pipe or even a wire boundary fence with steel poles or posts that's also fair game to include, the way to get a good earth is to be a sneaky barstard and take advantage of what's there.

The way we do it here is low tech using plenty of local labour. Dig the first meter by hand so you know you're not going to hit a supply cable or water main then use 2.4 meter long by 25mm rods that thread together knocked in with a 2-man slide hammer that weighs about 20 kilos. When the first rod is hammered in we use a brass threaded coupling to attach the second rod on top of it and sometimes even a third rod if the ground allows.

 

[pc1966]

@Marvo has excellent advice on earth rods, make sure you know there are no cables, pipes, sewer, etc, before driving them in! Also deeper is usually better so they are in permanently damp earth, however, your local soil characteristic really will determine what is practical.

However, I would say not to TT the installation unless you have fully separated E & N within the installation otherwise under open-PEN fault conditions you could find some "earthed" metal inside your home is live (at 230V or vaugely in that region) on the TN-C side while other metal that is TT will be on true Earth potential of 0V. Nasty!

If you keep it TN-C-S then in the UK at least the earth bonds to extraneous conductive parts such as service pipes and earth rods should be at least 10mm copper (or equivalent conductivity in other metals, 16mm Al or 80mm Fe, etc) to carry the high and persistent fault currents that open-PEN faults give rise to.

 

[pc1966]

Bear in mind our nearest neighbour is nearly a km away and the transformer even further.

Here you are unlikely to have other's current on an open-PEN fault, only your own installation.

I don't know how much lightning you get in that area but you might want to consider fitting the much more expensive type 1+2 SPD for overhead feeds, for example:

Type 1+2 Lightning Current and Surge Arrester (KM1+2-25-1+1 SC) - Kingsmill Industries

System: Single Phase TT/2 Pole Nominal Voltage: 230V AC

kingsmillindustries.com

That is suitable (and specified for) TT use but equally can be used on TN-S/TN-C-S, so it would allow any future decision on TT'ing the installation to go ahead without needing replacement.

 

[ivantheterrible]

@Marvo has excellent advice on earth rods, make sure you know there are no cables, pipes, sewer, etc, before driving them in! Also deeper is usually better so they are in permanently damp earth, however, your local soil characteristic really will determine what is practical.

However, I would say not to TT the installation unless you have fully separated E & N within the installation otherwise under open-PEN fault conditions you could find some "earthed" metal inside your home is live (at 230V or vaugely in that region) on the TN-C side while other metal that is TT will be on true Earth potential of 0V. Nasty!

If you keep it TN-C-S then in the UK at least the earth bonds to extraneous conductive parts such as service pipes and earth rods should be at least 10mm copper (or equivalent conductivity in other metals, 16mm Al or 80mm Fe, etc) to carry the high and persistent fault currents that open-PEN faults give rise to.

Thanks, that makes a lot of sense.

 

[ivantheterrible]

Thanks, that makes a lot of sense.

Hi again,
I'm now starting to think that it's actually a TT system I have, but frighteningly I can't find any earthing source on the property! I've included some pictures ... One and two, show the two single core cables coming in from overhead. The meter box is outside the property and was pictured earlier in this thread. Pictures three and four show the source cables coming into the fuse box, where the neutral is horribly combined with all the neutral lines coming in from plugs and lights ... These are piggy backed off of two main branches. Picture five shows the worst of the worst. Most connections are better than this, but it shows what I'm dealing with!

PS .... It looks like the pictures have uploaded in the reverse order

Any thoughts?