TNC installation - Continental Europe

Hi Andy, 

I doubt there is any bonding within the building as such to other services. There are definitely no bonding connections to water I know this much.

The main incoming supply I think would land directly into the matt:e with the N-E link being made across a DIN rail connector, using the model below: 

The L&N would connect to the incoming supply terminal, with a link from the N to the E. These 3 connections would then be switched via the contactor, providing a “protected” L,N,E connection. This would then land into the DB as normal, with the E straight to the earth bar and the L&N through a 2 pole RCD. 

Agree that voltage fluctuations may trip the matt:e device off, however i don’t foresee this being an issue. The supply voltage is pretty consistent and stable, the only reason for using the matt:e would be to add an additional layer of “protection” against lost/open PEN. As mentioned initially, the N conductors from all properties are all twisted together with a bit of tape around them - no really a solid bond as they are floating in free air! 

Thanks. 

I doubt there is any bonding within the building as such to other services.

Any class I appliances in contact with pipework? Immersion heaters, gas boilers, pumps, towel rail heaters, electric showers etc.? These may import potentials via the c.p.c. in the same way as bonding conductors.

   - Andy.

Interestingly the (presumably metallic) box's own earth is connected to the unprotected PE (which is probably correct in one way, given the possibility of a fault from the incoming conductors) - but that would mean that the box itself would likely be live under a broken PEN condition. That's probably fine for the intended use where the matt:e is indoors within the equipotential zone and it's just the EV/EVSE outside that needs disconnecting, but probably not what you want if you're trying to protect an entire installation.

   - Andy.

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

Hi Andy, 

There is an option for a plastic box, as well as a metal box with an RCD before the contactor, so in this instance the box’s earth could be connected to the output of the contactor so that the enclosure becomes disconnected during a PEN failure. 

There would be a small and insignificant risk of the incoming supply touching the metalwork, but I see this as unlikely, compared to someone climbing a ladder trying to reset an RCD which hasn’t tripped (not knowing the PEN fault is active).

I see a greater benefit in having PEN fault detection, because there is absolutely no way I would be able to ensure neutral connectivity downstream. It’s sort of a belt and braces approach. 

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! 

The building is made from concrete and there will be rebar within this concrete. A user would receive a shock in this instance

Are there no floor coverings? Some unglazed ties (e.g. quarry tiles) especially when often wet, were notorious for being 'earthy' but most other floor coverings seem to offer considerable resistance in practice. Not something you'd choose to rely on as such, but perhaps something to consider when weighing the actual risks...

         - Andy.

Hi Mike. Do you know which pictures are missing?

I see one in the OP of that link but I can’t make out where those that you think are missing would have sat within the replies? As far as I’m aware, no images are removed from posts once they age and I know we migrated images within posts from the previous community back in December 2021. So everything should be there? 

Hi Lisa thanks for coming back in on  a weekend, 

well the first is the image in the lead post though the text suggests it may actually have been a PDF

then there is a db picture with 3 single phase meters missing from the post  in the line between

Hey Chris, it is typical for the panel doors to be left unlocked like on this one also…

Missing picture
I will not b...

ah is it possible that the pics have gone but not the words, as the OP is 'former forum member'?

then these

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The apartment will be tilled throughout, directly onto a screed that sits on top of the concrete slab. The floors are around 400mm thick, with metal reinforcements, so the building as a hole is quite “earthy”. 

I will need to make a judgement call on this. I am not happy with the state of the incoming supply (the neutral), and the use of a PEN fault device can only add to the safety of the system I believe. They are a few hundred quid so it’ll be money well spent.

I am also kind of unsure how bonding the water will impact the rest of the building. The apartment is fed from a 4mm 3 core. If I take a 4mm bond to the water, I would in essence be proving bonding for the entire building so any stray currents from other apartments would undoubtedly find their way back into my installation.