TNC installation - Continental Europe

Can I ask which country - not all really do TNC-s, as the neutral integrity at the joints is not man enough to be safely split out to an earth, but rather expect TT. (or in some old eastern bloc buildings no obvious earth at all and single fault to danger)

Mike.

The county is Croatia. I can’t find any detail online about system earthing. If I look at overhead power lines around the cities and towns, there are only 4 cores (3 phases and neural). 

In all of the installations I’ve seen here over the years, there is a N-E link inside of the consumers DB. 

I now need to re-wire an apartment so need to get my head around this. 

Thanks. 

PS there are no earth rods anywhere. 

ah. I have not had anything to do with Croatian wiring at all. Some years ago  (nearly 20) the former East and west Germany and a bit of PL, and some French, but not anything  that far over. Ideally you need someone who knows both regs and practice, as I suspect, given the history, the two are likely to be a bit divergent.  

We had a discussion about an installation in Azerbaijan, here  but  for some reason the pictures have all been lost Lisa Miles  why is that ? Do pictures in a discussion rot after a year on the server ?

I think in his case we concluded that a TT install would be safer  It was horriffic - unsupport4ed joints shared neutralss etc. It may or may not be the same for you.

Mike.

 Mike

Thanks for this! Very helpful. 

A TT would be impossible as the apartment is on the 4th floor of a building. I will need to contact the supplier to find out exactly what is being supplied but won’t hold out on them being able to confirm! 

I am pretty confident it’s TNC to the consumers DB because all of the boards I have seen land N & E into the same terminals within the consumers DB and within the suppliers cupboard, all neutrals are joined - actually what is clear is that different installers have used a combination of different colours, including green/yellow for phase conductors! 

Will be interesting to see what the Ze is! 

Thanks. 

The killer question, quite literally, is how well you trust the joints in the  neutral between the transformer and your flat. The loss of any one is in effect an open circuit PEN, and all that entails in  terms of all the earthed metal work becoming live and nothing ever trips.  It is not an issue, perhaps, if all the services are non-conducting, gas/water/drains/TV antenna/ Telephone etc  and cannot introduce a true earth potential  to be at odd with the neutral derived one. Even then one has to watch out for structural steels and rebar.

Earth rods as per the BSI are not the way in Germany either, but connection to the foundations is pretty common and more or less universal on modern buildings, as well as all the usual pipe bonding, so their NE split is in effect accompanied by a large electrode.

Does your flat get all 3 phases or just one ? if you get all 3 you can detect severe neutral wander.

Mike.

Thanks Mike.

Its single phase and neutral, so no way to measure phase/neutral issues. 

I wonder, if a matt:e would be an ideal solution? I know they are designed for EV installations, however do offer PEN fault removal and will negate the need for an earth rod. They will in essence disconnect L+N, which will then completely isolate the installation from the grid.

The N-E bond would be made on the incoming of the matt:e. 

It would be really impractical to install an earth rod for the apartment.

This would then mean, that the phase conductor needs to land into this MCB before the RCD. Is a single pole MCB really the best choice, or should I look to use a double pole MCB that disconnects the phase and the neutral conductor, and if so, what then happens to the earth?  

The general principle is that the path of the PEN to the earth bar should be as solid and reliable as possible - certainly not running through any protective device or switch. If i recall correctly, some places that do MEN (multiply earthed N) - e.g. Aus/NZ tend to take the PEN to the earth bar first and then link to the N. After the N-PE split, you can then switch the N as much as you like (along with L of course, not SP) - but to be honest if all the metalwork in the place is bonded to the supply N anyway, there seems little advantage in DP switching even for isolation upstream of RCDs.

Just check that there aren't any other N-PE splits about the place - E Germany used to be famous for sockets being supplied by 2-core cables with one wire going to both N and PE contacts - and I guess they weren't unique in that. Such things will upset RCD protection good and proper.

   - Andy.

Thanks Andy. That makes sense. 

I asked above but maybe you know. Would the install of a matt:e at the start of the installation reduce the likelihood of an open PEN? The main feed would come in, and would be connected via the matt:e.

The N-E bond can happen inside of this box, between PE and N.

I know these devices are certified in the UK for EV charge points, but I don’t see why they couldn’t in this instance be used for an extra layer of protection?

Would the install of a matt:e at the start of the installation reduce the likelihood of an open PEN?

It wouldn't reduce the likelihood of an open PEN occurring, it might provide a bit of protection for your installation by disconnecting everything (including the Earth) if it did happen though.

That said, if there are any shared metallic services with the rest of the building, it's likely to be defeated by main bonding etc. re-introducing the hazardous voltage from other parts of the building. Also most of the open PEN detectors work by measuring L-N voltage - if the supply system is as dodgy as everything else and you get large voltage variations in normal use - which might potentially fool the device into thinking there was a PEN problem when there wasn't - so it might be prone to nuisance tripping.

Also the risk/benefit is probably a bit different to an EV - inside a building you can usually achieve a half decent equipotential zone so the risk of shock from a broken PEN event is much reduced anyway - while on the other hand you're introducing a set of mechanical contacts in the earthing system which almost inevitably will be less reliable than a single bolted joint.

   -  Andy.