TNCS - USING NEUTRAL AS EARTH IN BOARD

[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?