Understanding the relationship between TNCS, TNS and TT

[HappyHippyDad]

I have never actually had to make an electrical system into a TT. I have added rods in order to get an effective Ra but never had to (for example) install a TT on a new garage or shed.

It's best I give an example with regards my question..

A new garage has a supply taken to it from the house. The house is PME and this has been extended to the garage, lets say 4mm 3 core SWA. The 3rd core is perfectly adequate as an earth. Also, the installer puts a copper rod in the ground and attaches this to the earth bar in the new garage CU. Is this OK? Is this actually better? Is it now dangerous?

I've got a few ideas but I'd rather not influence the line of thought and just leave it as above.

Cheers all.

 

[pc1966]

I want to ask now. Why is TN-S being phased out? What was the technical justification for abandoning a previous method that worked better?

Cost.

Remember their cost decision is about delivering power, not considering the implications for more expensive EV chargers, etc., for those using the power.

 

[Cookie]

Cost.

Remember their cost decision is about delivering power, not considering the implications for more expensive EV chargers, etc., for those using the power.

I figured. However, wasn't the UK poor as compared to the economic prosperity of today when TN-S was the norm?

 

[DPG]

I figured. However, wasn't the UK poor as compared to the economic prosperity of today when TN-S was the norm?

Yes, but I don't think TNCS had been thought of at that time.

 

[Cookie]

Yes, but I don't think TNCS had been thought of at that time.

It had been in other parts of the world. I could be wrong but East Germany and Russia was TN-C all the way up to the socket.

 

[DPG]

It had been in other parts of the world. I could be wrong but East Germany and Russia was TN-C all the way up to the socket.

Not TNCS though.

 

[Cookie]

Not TNCS though.

I'm sure those building networks in the UK would had to have known of a PEN conductor by the 40/50s? I want to think there was a technical decision behind TN-S.

 

[LastManOnline]

Yes, but I don't think TNCS had been thought of at that time.

What's not to think of? All supply systems are relatively simple to design and weigh up regarding pro, s and cons. TNC-S as, a supply system has been there as long as the others but can you imagine been the electrical engineer who suggested it....
[automerge]1600011608[/automerge]

Cost.

Remember their cost decision is about delivering power, not considering the implications for more expensive EV chargers, etc., for those using the power.

Agreed. It was an economic decision. Very smart in the short term but long term........ (sighs!!)

 

[Simon47]

Thinking about it a little, put yourself in the shoes of those running the distribution networks "a few years back". AIUI they typically didn't provide an earth, so the distribution network was 4 core, and 2 core to the single phase customers.
Then along came plastic gas and water pipes. Customers (or their electricians, or the builders putting houses up) had become used to having a solid earth via the water supply - and this was becoming an unknown factor. At the same time I suspect, people were starting to think more about safety - and just banging a token rod in the ground was no longer acceptable for installation earthing.
So "people" start looking to the DNOs and asking why there's no earth being provided, and at some point (AIUI) the DNOs were told they had to start providing earths. Logically, it's the place to provide an earth - they have long runs of underground cable (which at the time would have been mostly lead sheathed), and for overhead supplies they have plenty of poles they can put an earth rod in close to to make a distributed earthing system.
Where they have 4 core lead sheathed in the ground, it's easy to provide an earth - but there's no guarantee that the sheaths are electrically linked at every joint. If it's not got a conductive sheath then that's a different matter. And overhead supplies would have been typically two or four uninsulated cores strung from pole to pole. So what are they supposed to do in these situations ?
Overhead they could string another wire - as long as none of the spans are marginal for height. But if there's an insulated underground section then the only way to add an earth core would be to start digging. And in urban areas with typically underground supplies, that's a lot of digging to do. Basically, adding a separate earth to sections of the network that don't already have one is a massively expensive task.

So if you look at the cost involved of providing a separate earth across the network, you can understand why combined N&E looked attractive. And even when building a new bit of network, you've eliminated a 5th core - which even allowing for it perhaps being a smaller CSA, is a big saving in copper.
And if you have (e.g.) lead sheathed cables in the ground, just linking the neutral to sheath at some joints immediately gives you a strong earth - without having to go round checking for sheath bonding across all joints.

 

[LastManOnline]

Thinking about it a little, put yourself in the shoes of those running the distribution networks "a few years back". AIUI they typically didn't provide an earth, so the distribution network was 4 core, and 2 core to the single phase customers.
Then along came plastic gas and water pipes. Customers (or their electricians, or the builders putting houses up) had become used to having a solid earth via the water supply - and this was becoming an unknown factor. At the same time I suspect, people were starting to think more about safety - and just banging a token rod in the ground was no longer acceptable for installation earthing.
So "people" start looking to the DNOs and asking why there's no earth being provided, and at some point (AIUI) the DNOs were told they had to start providing earths. Logically, it's the place to provide an earth - they have long runs of underground cable (which at the time would have been mostly lead sheathed), and for overhead supplies they have plenty of poles they can put an earth rod in close to to make a distributed earthing system.
Where they have 4 core lead sheathed in the ground, it's easy to provide an earth - but there's no guarantee that the sheaths are electrically linked at every joint. If it's not got a conductive sheath then that's a different matter. And overhead supplies would have been typically two or four uninsulated cores strung from pole to pole. So what are they supposed to do in these situations ?
Overhead they could string another wire - as long as none of the spans are marginal for height. But if there's an insulated underground section then the only way to add an earth core would be to start digging. And in urban areas with typically underground supplies, that's a lot of digging to do. Basically, adding a separate earth to sections of the network that don't already have one is a massively expensive task.

So if you look at the cost involved of providing a separate earth across the network, you can understand why combined N&E looked attractive. And even when building a new bit of network, you've eliminated a 5th core - which even allowing for it perhaps being a smaller CSA, is a big saving in copper.
And if you have (e.g.) lead sheathed cables in the ground, just linking the neutral to sheath at some joints immediately gives you a strong earth - without having to go round checking for sheath bonding across all joints.

I appreciate your points and likewise I appreciate the dilemma the various DNOs were presented with and obviously a, solution had to be arranged. I can, t comment on the situation in the UK but I do not believe it is satisfactory here (ROI) where it is becoming almost exclusively TNC-S to accept that we must now regard the risks associated with a broken neutral as the "new norm".
If the DNO is not for whatever reason in a position to provide a solution let's at least as an industry "front up" about the reality of the situation and start looking at ways to solve the issue from the homeowners standpoint.
I don't want to go into any detail about possible solutions, as its been discussed already extensively (and very adequately) on this and other threads. I can appreciate that there may be a degree of "fatigue" setting in. But I will say this. If I am to hear that the UK is going to follow our lead (and Aus, NZ) etc and implement the "four foot" rod (AKA "the fig leaf), I will despair ?. COOKIE, Are you out there? Time to launch a transatlantic campaign to fully TNC-S?
[automerge]1600024143[/automerge]

I appreciate your points and likewise I appreciate the dilemma the various DNOs were presented with and obviously a, solution had to be arranged. I can, t comment on the situation in the UK but I do not believe it is satisfactory here (ROI) where it is becoming almost exclusively TNC-S to accept that we must now regard the risks associated with a broken neutral as the "new norm".
If the DNO is not for whatever reason in a position to provide a solution let's at least as an industry "front up" about the reality of the situation and start looking at ways to solve the issue from the homeowners standpoint.
I don't want to go into any detail about possible solutions, as its been discussed already extensively (and very adequately) on this and other threads. I can appreciate that there may be a degree of "fatigue" setting in. But I will say this. If I am to hear that the UK is going to follow our lead (and Aus, NZ) etc and implement the "four foot" rod (AKA "the fig leaf), I will despair ?. COOKIE, Are you out there? Time to launch a transatlantic campaign to fully TNC-S?

Sorry fourth sentence should read" NOT satisfactory"

 

[Cookie]

I appreciate your points and likewise I appreciate the dilemma the various DNOs were presented with and obviously a, solution had to be arranged. I can, t comment on the situation in the UK but I do not believe it is satisfactory here (ROI) where it is becoming almost exclusively TNC-S to accept that we must now regard the risks associated with a broken neutral as the "new norm".
If the DNO is not for whatever reason in a position to provide a solution let's at least as an industry "front up" about the reality of the situation and start looking at ways to solve the issue from the homeowners standpoint.
I don't want to go into any detail about possible solutions, as its been discussed already extensively (and very adequately) on this and other threads. I can appreciate that there may be a degree of "fatigue" setting in. But I will say this. If I am to hear that the UK is going to follow our lead (and Aus, NZ) etc and implement the "four foot" rod (AKA "the fig leaf), I will despair ?. COOKIE, Are you out there? Time to launch a transatlantic campaign to fully TNC-S?
[automerge]1600024143[/automerge]

Sorry fourth sentence should read" NOT satisfactory"

I'm still here!

See my other thread, I may have a solution for full TN-S!

 

[LastManOnline]

I'm still here!

See my other thread, I may have a solution for full TN-S!

Good to hear?

 

[Cookie]

Good to hear?

Yup, and following along.

To add to this thread- few have stop to think what stray current flowing all over the earth and infrastructure is doing...

 

[LastManOnline]

I'm still here!

See my other thread, I may have a solution for full TN-S!

What's the title of your other thread..?

 

[Cookie]

What's the title of your other thread..?

"practicality of 400 volt equipment"