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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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    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.

  • 0 in reply to AJJewsbury

    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?

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  • 0 in reply to AJJewsbury

    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?

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