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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. 

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  • 0

    well if the rising water pipe is metallic it may well be a better representation of true earth potential than the neutral of the mains supply.  Same for gas and if the drainage stacks are metallic.

    As above, no detector is going to prevent a lost neutral event, the only thing that can do that is doubly crimped neutrals and all the other stuff we do on the distribution network these days. Even then we get a few hundred a year.  But I'm sure you knew that.

    The bigger question is how much to disconnect if you detect a lost neutral, and how to avoid straddling parts at different voltages. To that end  bonding the plumbing and any other services, as well as any exposed building steel etc is probably more use - you do not care too much if it all goes live together, even while you are touching it, the problem is when only half of it does and you are the link  that completes the current path.

    Mike

  • 0 in reply to mapj1

    Hi Mike,

    I agree that preventing a lost neutral would be impossible as this is out of my control entirely. The idea of bonding doesn’t exist here but would make sense. 

    There is literally a water supply and a telecoms connection, no gas or exposed structural metalwork and new pipe work would be plastic back to the main supply which would be in a locked cupboard. 

    My biggest concern would be a class 1 appliance becoming live during an open PEN, and a user touching this and receiving a shock. The building is made from concrete and there will be rebar within this concrete. A user would receive a shock in this instance; bonding pipes wouldn’t remove this risk hence why fully disconnecting the installation to me at least seems like a belt and braces approach. 

    A PEN fault in the UK may be rare, but in Croatia more likely because of the suppliers connection methods, and the fact the systems are aged, and held together with tape rather than screws! 

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  • 0 in reply to mapj1

    Hi Mike,

    I agree that preventing a lost neutral would be impossible as this is out of my control entirely. The idea of bonding doesn’t exist here but would make sense. 

    There is literally a water supply and a telecoms connection, no gas or exposed structural metalwork and new pipe work would be plastic back to the main supply which would be in a locked cupboard. 

    My biggest concern would be a class 1 appliance becoming live during an open PEN, and a user touching this and receiving a shock. The building is made from concrete and there will be rebar within this concrete. A user would receive a shock in this instance; bonding pipes wouldn’t remove this risk hence why fully disconnecting the installation to me at least seems like a belt and braces approach. 

    A PEN fault in the UK may be rare, but in Croatia more likely because of the suppliers connection methods, and the fact the systems are aged, and held together with tape rather than screws! 

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