TNCS - USING NEUTRAL AS EARTH IN BOARD

[assegayer]

Im travelling abroad to a country that has no earthing arrangement and my friend would like me to do a bit of work on his house. My question is Whether or not i could create a link between the Neutral and Earth bar to create a tncs system.

I know it sounds strange but i have just been thinking for the past couple of days how they do it here in the uk. They do the same thing for tncs systems a link between neutral and earth.
Could someone shine some light on the subject as to why it cannot be done and how it can be done here then?

P.s i know a earth rod can be hit into the ground but want to explore all options.

Thanks

 

[westward10]

What country is it, you couldn't do it here but you would need to comply with the Regulations/Codes of that country.

 

[assegayer]

There really are not any codes or regulations there. But we are talking away from any code or regs..just in terms of would it work, be safe and practical. Forget about regs for the moment

 

[Pete999]

What country is it, you couldn't do it here but you would need to comply with the Regulations/Codes of that country.

What he said^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 

[Pete999]

There really are not any codes or regulations there. But we are talking away from any code or regs..just in terms of would it work, be safe and practical. Forget about regs for the moment

Wash yer mouth out you naughty boy "forget the regs"

 

[assegayer]

There honestly no regs there i just want to know for my own inforation because no one can ever give me a informative answer

 

[Octopus]

What Country are you talking about?

 

[assegayer]

Libya

 

[Octopus]

Libya

Why didn't you state this in the OP?

 

[Des 56]

I know nothing of other countries,but here the star point of the supply transformer is connected to earth and spiked along its run to keep it at or close to earth potential
Probably,the star point is earthed
If the supply then comes direct without the neutral and earth being spiked,its then jointed at the load end,the property earth and the true earth may be at very different potentials

Just seen its Libya, Do they still have properties standing in that sorry land ?

 

[assegayer]

Its not really that relevant to the question its an electrical science question which no one has answered yet unfortunatly

 

[assegayer]

I know nothing of other countries,but here the star point of the supply transformer is connected to earth and spiked along its run to keep it at or close to earth potential
Probably,the star point is earthed
If the supply then comes direct without the neutral and earth being spiked,its then jointed at the load end,the property earth and the true earth may be at very different potentials

Just seen its Libya, Do they still have properties standing in that sorry land ?

Thanks for answering the queston, many still happilly standing

 

[westward10]

I would be very cautious about creating your own TN-C-S system because as Des says over here it has to confirm with specific requirements to keep the PEN at a reasonable resistance to true earth. Not knowing the setup in Libya you would be taking a huge risk doing this particularly with the hazards known with regards to a lost neutral which happens here and who knows the system reliability there.

 

[assegayer]

I would be very cautious about creating your own TN-C-S system because as Des says over here it has to confirm with specific requirements to keep the PEN at a reasonable resistance to true earth. Not knowing the setup in Libya you would be taking a huge risk doing this particularly with the hazards known with regards to a lost neutral which happens here and who knows the system reliability there.

You see this is where i cant get me head round it. Because in the uk they have tncs which is just a link , why can it not be done in every uk home. It also has the same risks as anywhere in the world for example loss of neutral.

 

[assegayer]

Why for example is it different i a home where its tns . Theoretically couldnt i just not use the swa sheath as earth and just use a linkbetween live and neutral. I hope you can make some sense of what im saying

 

[Wilko]

Where angels fear to tread ... I'd test it but probably go with RCD and TT at the home end. Making the outside of your coffee machine the same potential as the neutral in an unregulated environment is asking for a zap, IMHO.

 

[assegayer]

But then why is it done in the uk the same problems can happen here????

 

[Wilko]

UK currently not war torn and so we can rely upon the earth provided by the Distribution Network Operator. If DNO does not provide one, then TT and RCD is the go

Just to add a plug - it's only reliable because of the strict application of standards by hard working expert engineers keeping the UK distribution network in top shape. Sounds a bit corny but it is true, again IMHO.

 

[westward10]

But then why is it done in the uk the same problems can happen here????

Yes they can and it does but it is deemed an acceptable risk. But as Wilko says how regulated is the supply there because we have strict guidelines for PME here and that is not foolproof.

 

[assegayer]

UK currently not war torn and so we can rely upon the earth provided by the Distribution Network Operator. If DNO does not provide one, then TT and RCD is the go

No thats not what i mean , forgot war and all that. Why is it that a in one house a tncs system here can be connected to neutral but in another house it cant?

 

[assegayer]

No thats not what i mean , forgot war and all that. Why is it that a in one house a tncs system here can be connected to neutral but in another house it cant?

Isnt all neutals connected to earth at the very begining anyway?

 

[mhar]

Our network is planned and has multiple earth points. There are rules, for instance I think it is every third or fourth pole must be earthed. On tncs we are channeling the fault currents through the network, seems like a good idea to me that we know that the network can take it and not just hope

 

[assegayer]

Our network is planned and has multiple earth points. There are rules, for instance I think it is every third or fourth pole must be earthed. On tncs we are channeling the fault currents through the network, seems like a good idea to me that we know that the network can take it and not just hope

So the neutral is earthed every third or fourth pylon to keep the resistance down?

 

[westward10]

I don't know the intervals and it may vary but the resistance between the neutral and true earth used to have a required maximum resistance of 20 ohm.

 

[The Ghost]

Not all the supply systems are the same. Some are very old and do not suit PME and cannot be upgraded. Systems put in place over a hundred years ago are not suitable for PME now and are being disconnected where possible, and upgraded again where possible. Not all supplies are straight forward three phase supplies due to historical diabolical methods of supply.

 

[buzzlightyear]

many still happilly standing

what tents .

 

[Midwest]

He he he, I had an SSE engineer round to look at a possible dodgy TN-S supply and asked if it could be changed to TN-C-S. Said it could, but 'you'd need to wait 5 weeks, why not do it yourself?', 'Que???'. He then went onto demonstrating connecting EC into neutral of service head .

I didn't, but kept his name in my little black book, for when I need a get out jail card.

 

[mhar]

He he he, I had an SSE engineer round to look at a possible dodgy TN-S supply and asked if it could be changed to TN-C-S. Said it could, but 'you'd need to wait 5 weeks, why not do it yourself?', 'Que???'. He then went onto demonstrating connecting EC into neutral of service head

Hmm. When my youngest was a linesman I asked him if he would remove a knockout on a bakerlite service head as I wanted to upgrade the Earthing conductor to 16mm, Ze was something like .20. His manager gave him permission so he opened it up and was suprised to see a split con cable feeding the head (definitely no n-e link) so the supply was tns although it appeared to be tncs. Out of interest I got the same Ze reading when both n & e leads were on the supply n as when putting the leads on the individual l, n & e conductors. The feed for next door was taken from this service head and someone had done a homemade earth to neutral connection assuming that pme was available. He enquired of the network planner who was insistent that the network would not support tncs and that next door must be tt'd (we were fine as tns). My son wasn't expecting this response, freely admitted that taken in isolation he would probably have thought that next doors supply was ok, and conceded that the only person who would really know the answer to such a query is the network planner responsible for the area.
Only the network planner can tell you whether pme is available. It is so easy to make an earthing enquiry it is stupid to not do it right

 

[Darkwood]

On the same lines as mhar, an assessment of the network conditions and type are crucial to allow for the permittance of a PME/TNCS conversion, the safety of the user, property as well as other users may be at risk if this is done by anyone but the DNO, we have 10's of thousands of miles of old degrading network cables and joints that won't be suitable, although I cannot comment on other countries and their own systems and regulations I can say that under no circumstances should anyone try to do their own conversion even if its just hypothetical, that puts a hypothetical family at risk and its just not worth thinking about let alone undertaking such a task.

 

[Midwest]

Only the network planner can tell you whether pme is available. It is so easy to make an earthing enquiry it is stupid to not do it right

I didn't do it

His argument, was my TN-S supply was probably turned into TN-C-S in the road outside. Whenever, the DNO repair an old cable, it's always turned into PME.

 

[mhar]

@Midwest, comment most definitely not aimed at you but for general consumption.

'Probably turned into tncs' is not a statement I would rely upon

 

[Had8Lives]

Isnt all neutals connected to earth at the very begining anyway?

I was told by a Part P assessor that a couple of reasons for the DNO not providing a PME earth was 1) Because of the risk of lightning strikes in some areas and 2) neutral currents

 

[hightower]

If RCDs are used, and you create the link from the neutral bar(s) to earth (as in your OP), the RCD then will not see any fault current and will fail to operate, because any earth fault is directed back down neutral before it passes through the RCD.

 

[PEG]

Just a minor point,but the OP never mentioned what type of supply we were discussing,could be national,local or private generation...will affect any earthing decisions directly.

 

[Risteard]

Why is it that a in one house a tncs system here can be connected to neutral but in another house it cant?

It's connected to a PEN conductor - not any old neutral!

 

[assegayer]

If RCDs are used, and you create the link from the neutral bar(s) to earth (as in your OP), the RCD then will not see any fault current and will fail to operate, because any earth fault is directed back down neutral before it passes through the RCD.

Would still work though in the sense rhat if you were to touch a live conductor it would trip

 

[assegayer]

Thank you to everyone who has taken the time to reply. You have given me a greater insight into the topic

 

[Deleted member 26818]

If RCDs are used, and you create the link from the neutral bar(s) to earth (as in your OP), the RCD then will not see any fault current and will fail to operate, because any earth fault is directed back down neutral before it passes through the RCD.

RCDs don't detect fault current, they detect imbalances between Line and Neutral.
The Neutral Earth link is placed up stream from any RCD, which prevents any earth Fault Current from bypassing the RCD via the Neutral.

To the OP, with TN-C-S in this country, a single conductor is used to carry Neutral and Earth Fault Currents. Not two conductors joined together.
The link between Neutral and Earth is put there to allow the installation earth a path back to the Transformer.
What you suggest would work, and if were only a single installation with the link, it would be unlikely to have any adverse affect on the distribution system.

 

[hightower]

RCDs don't detect fault current, they detect imbalances between Line and Neutral.
The Neutral Earth link is placed up stream from any RCD, which prevents any earth Fault Current from bypassing the RCD via the Neutral.

The OP specifically said the link would be in the bus bar, which on the boards I've worked with would be before any RCD. That way fault current returns through the neutral and through the RCD as normal current would, and the RCD would not operate.

 

[hightower]

Would still work though in the sense rhat if you were to touch a live conductor it would trip

Say what?

 

[telectrix]

No thats not what i mean , forgot war and all that. Why is it that a in one house a tncs system here can be connected to neutral but in another house it cant?

because where PME is provided, the supply has the N (star point) reliably earthed at several points along it's route. therefore, it's maintained at ground potential. best option is to TT it with RCD for fault protection, as wilko stated .

 

[Deleted member 26818]

The OP specifically said the link would be in the bus bar, which on the boards I've worked with would be before any RCD. That way fault current returns through the neutral and through the RCD as normal current would, and the RCD would not operate.

Yes, creating the link at the busbar, or anywhere down stream from the RCD would cause the RCD to trip whenever power was used.

 

[hightower]

Yes, creating the link at the busbar, or anywhere down stream from the RCD would cause the RCD to trip whenever power was used.

Pretty sure it would cause it to never trip even under fault. Gonna draw this out tonight....

 

[hightower]

Okay, so the scenario in the OP was that a link was made between the earth and neutral bus bars. This is my interpretation of that, as depicted by the purple line. (Apologies about the Paint job, not quite Richard Burns spec).

My question is Whether or not i could create a link between the Neutral and Earth bar to create a tncs system

So current flows through the line through the RCD, and out on the first circuit. There's a fault, and it returns via the earth path. The earth path is linked to neutral before it passes through the RCD, and the current then passes through the neutral via the RCD. The RCD wouldn't see a fault and doesn't operate.

View attachment 35580

 

[Deleted member 26818]

You won't get to the fault stage, as the RCD will operate as soon as any power is used.
Some of the return current will return to the power supply via the earth instead of via the neutral.
The RCD will see the imbalance between the Line and neutral and trip.

 

[hightower]

You won't get to the fault stage, as the RCD will operate as soon as any power is used.
Some of the return current will return to the power supply via the earth instead of via the neutral.
The RCD will see the imbalance between the Line and neutral and trip.

What earth? There is no earth, it has been linked to neutral to create a bodged TNCS

 

[Rpa07]

You've only got to think of the scenario of wrong neutral leg to wrong neutral bar or when you're working on a circuit switched off at the board but neutral not removed, so easy to trip if neutral and earth touch. The amount of imbalance needed through the RCD coils is minuscule to cause a trip. No way would the install be a happy install if @hightower 's scenario was attempted.

 

[hightower]

You've only got to think of the scenario of wrong neutral leg to wrong neutral bar or when you're working on a circuit switched off at the board but neutral not removed, so easy to trip if neutral and earth touch. The amount of imbalance needed through the RCD coils is minuscule to cause a trip. No way would the install be a happy install if @hightower 's scenario was attempted.

I'd argue quite the contrary - it would be too happy, and would render the RCD completely useless.

 

[Rpa07]

It's electrickery, it knows more than us! We're just wire monkeys! I understand your passion though - we need a "myth buster"

 

[westward10]

Might try this tomorrow, it a controlled environment obviously