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TNC installation - Continental Europe

vantech
  1. Hi,

I am looking at re-wiring a small apartment on the continent. The supply to the building is a TNC.

I was quite surprised to find a 4 core 6mm cable coming into the building from an underground cable, with the 3 phases landing into 80A fuses and the neutrals twisted together with an aged bit of tape around them. There are then multiple 4mm cables that connect to the secondary side of these fuses, which go off to the various properties.

The properties themselves have a consumer DB, with the phase conductor landing in a 32A MCB. The neutral then lands into the neutral bar, with a link to the earth bar.

I just wanted to clarify the following. 

Q1: 

When upgrading this apartment, I obviously want to use RCDs. I believe in order to do this, I would need to land the incoming neutral into a suitable connector, which then links to the neural terminal of the RCD and also the earth bar - this would then give me a TNC-S earth and neutral. The neutral output of the RCD is then in essence measured and compared to the phase conductor for subsequent outgoing circuit protection. 

Q2: 

I am assuming that the supply authority rely solely on the consumers “main switch” which is in essence an MCB to ensure the cable between the suppliers main feed and the property isn’t overloaded, because the suppliers fuses are not rated to protect the 4mm cable that comes into the property. I believe they have rated the fuses high enough to cope with the maximum demand for the connected properties. 

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?  

Obviously all of this falls outside of BS7671, because this standard doesn’t apply on the continent. I am just looking to clarify my understanding. I have actually looked at various installations and all of them are the same. The standard of wiring and associated safety devices/methods doesn’t even compare to what we do in the UK.  

I have also looked at using a local electrician - really not an option considering the state of some of the installations I’ve seen! 

Thanks. 

Parents
  • 0

    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   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

  • 0 in reply to mapj1

    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. 

  • 0 in reply to vantech

    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.

  • 0 in reply to mapj1

    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.

Reply
  • 0 in reply to mapj1

    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.

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