UK TT undetectable PEN fault

[Hakuhou]

As already said the Earth rod is connected before the Consumer unit so all the rod is doing is adding to the PME earthing.

If the Rod was connected to the earth bar in the Consumer unit and penetrated the Neutral, it would no longer be a TNC-S as there would be no Separation from the earth bar.

Thank you, getting there.
So this is a TN-S system but where the installation’s earth has been connected to the “first” earth in the PME chain.

 

[DefyG]

current will always take the path of least resistance which is most unlikely to be your new earth rod.

Probably should have said 'most' as the earth rod having a significantly higher resistance, the current would be insignificant (probably) but this is all hyperthetical!

 

[Tom256]

Thank you, getting there.
So this is a TN-S system but where the installation’s earth has been connected to the “first” earth in the PME chain.

View attachment 119470

That is not TN-S. Do you understand why?

 

[Hakuhou]

Current flows through all paths in an amount inversely proportional to their resistance.

Ohm’s law right? V=I/R

 

[DefyG]

Ohm’s law right? V=I/R

Wrong

 

[Hakuhou]

That is not TN-S. Do you understand why?

Hmm, for TN-S the installation earth is directly connected to the source earth (usually via the DNO’s supply cable’s metal sheath, this is not the case so not TN-S.
For TN-C-S the separate bit is missing
So yes not TN-S, but not TN-C-S since the S is missing.
By process of elimination it’s a TN-C, in the book I read.
“TN-C is not generally permitted in the UK.”
Ok time to read up on TN-C.

 

[Hakuhou]

Wrong

Typo V=IR -> I=V/R

 

[Tom256]

Hmm, for TN-S the installation earth is directly connected to the source earth (usually via the DNO’s supply cable’s metal sheath, this is not the case so not TN-S.
For TN-C-S the separate bit is missing
So yes not TN-S, but not TN-C-S since the S is missing.
By process of elimination it’s a TN-C, in the book I read.
“TN-C is not generally permitted in the UK.”
Ok time to read up on TN-C.

Consider the 'S' in TN-C-S. What part of the electrical system does this aspect apply to? Where do the neutral and the protective earth become separated never again to come together?

 

[Tom256]

Consider the 'S' in TN-C-S. What part of the electrical system does this aspect apply to? Where do the neutral and the protective earth become separated never again to come together?

To help with your consideration of this. Using your diagram in post #21.
The earth point on that 3rd electrode (closest to the installation) was moved along by some form of pixie a tad and was now at the origin of the customers installation.

 

[mainline]

Hmm, for TN-S the installation earth is directly connected to the source earth (usually via the DNO’s supply cable’s metal sheath, this is not the case so not TN-S.
For TN-C-S the separate bit is missing
So yes not TN-S, but not TN-C-S since the S is missing.
By process of elimination it’s a TN-C, in the book I read.
“TN-C is not generally permitted in the UK.”
Ok time to read up on TN-C.

For it to be TT earthing, you would have to have the ROD connected to the earth bar in the consumer unit.

The PEN would be isolated from that consumer unit.

 

[Hakuhou]

What part of the electrical system does this aspect apply to?

S refers to the installation side, whereby the earth and neutral returns are “Separate” on this side.

Where do the neutral and the protective earth become separated never again to come together?

The neutral and earth separate at the intake of the installation.

Just searched youtube and found a video for you that may help with your understanding. I have not watched it through but from my quick scan through it covers one of the points you have raised:

View: https://www.youtube.com/watch?v=z7han_twcnw

This was interesting. The PEN fault at neighbor 2 meant that their neutral was returning through their earth, into the metal services, into neighbor 1’s and then into neighbor 1’s earth-neutral link.
When neighbor 1 disconnected their earth neighbor 2’s electrics stopped, with the added drama of this energizing everything connected to the earth systems of both neighbors.

To help with your consideration of this. Using your diagram in post #21.
The earth point on that 3rd electrode (closest to the installation) was moved along by some form of pixie a tad and was now at the origin of the customers installation.

I’m still thinking about what kind of earth system it would be. I think that a TT that is connected back to a TN-C-S (e.g. via some metal pipe work that’s been earthed by both systems) is an extension of that TN-C-S.

After reading all this my question becomes, what happens if the earth electrode in what is intended to be a TT system connects/is not sufficiently insulated from the CNE.
The CNE is used by other installations (e.g. other houses) as part of their TN-C-S systems.

 

[mainline]

I’m still thinking about what kind of earth system it would be. I think that a TT that is connected back to a TN-C-S (e.g. via some metal pipe work that’s been earthed by both systems) is an extension of that TN-C-S.

Its still a TT.

 

[mainline]

After reading all this my question becomes, what happens if the earth electrode in what is intended to be a TT system connects/is not sufficiently insulated from the CNE.
The CNE is used by other installations (e.g. other houses) as part of their TN-C-S systems.

It may prevent a protective device from operating.

 

[buzzlightyear]

View: https://youtu.be/z7han_twcnw