TNS supply Ze at 1.7ohm

[JohnW2]

Nope

All I can say is that a lot of people seem to say (and believe) that - but perhaps you are the only one who is actually correct.

 

[Murdochcat]

All I can say is that a lot of people seem to say (and believe) that - but perhaps you are the only one who is actually correct.

Just experience at the coal face over many years

 

[securespark]

My understanding is that if there is a DNO-supplied TN earth, then they are obliged to 'maintain' it (which, in the case of TN-S, often means changing it to TN-C-S) ??

Kind Regards, John

If the earthing facility has been installed by the DNO, then yes, they have a duty to maintain it.

But they don't usually change the supply type.

Occasionally, IME, DNOs have upgraded TT supplies to TN-C-S on request, providing the infrastructure is suitable.
Sometimes they have done this for free, other times for a small charge.

 

[securespark]

try againView attachment 336664

If that's your supply coming into the box marked 415V, it doesn't look like SWA.

It appears to have a copper strap round it.

 

[Olivias Grumpy]

So much higher could it be to be acceptable?
Before the CU was changed, the flat has been owned by my wife’s mum, and now us since 1994
Never had a fuse blow. Never even changed a light bulb for mum

 

[Olivias Grumpy]

If that's your supply coming into the box marked 415V, it doesn't look like SWA.

It appears to have a copper strap round it.

I would describe as a wrap around P clip with a pinch bolt. I think it is copper or maybe brass?
I’ll ask my electrician if he knows.

However my first question remains
Is Ze of 1.7ohm ok?

 

[securespark]

That would depend on whether the supply is maintained by the DNO. What did your spark say should be done about it?

 

[Olivias Grumpy]

He is asking same questions elsewhere

 

[JohnW2]

If the earthing facility has been installed by the DNO, then yes, they have a duty to maintain it.

As I said, that has always been my understanding, but it appears that if one has "many years of experience at the coal face" one 'knows' that it is not true!

But they don't usually change the supply type.

I know of many cases in which DNOs have addressed thee issue of a TN-S earth having become inadequate by converting it to TN-C-S. I thought that that practice,which some people here have described that as a 'lazy' or 'cheapskate', was common?

Occasionally, IME, DNOs have upgraded TT supplies to TN-C-S on request, providing the infrastructure is suitable. Sometimes they have done this for free, other times for a small charge.

That's obviously a bit different,since if it's TT, then the DNO have never provided an earth.

I have to say that, after my local distribution network was PMEd, I have more than one been offered (almost 'encouraged') to have my TT installation converted to TN-C-S , without charge - although I have always declined those offers.

Kind Regards, John,

 

[JohnW2]

Just experience at the coal face over many years

I see.

 

[JohnW2]

However my first question remains Is Ze of 1.7ohm ok?

It's a bit more than double what most people seem to regard ads 'the maximum' for TN-S.

Whether allowed or not, a Ze of that value would preclude having any circuits greater than 20A, and may not even be adequate for longish 20A circuits (or long 16A ones -unless one used unusually large cables. In other words, it would be 'impractical'

 

[securespark]

As I said, that has always been my understanding, but it appears that if one has "many years of experience at the coal face" one 'knows' that it is not true!

I have had many years of experience and the DNO have always sorted issues with their earth connections.

I know of many cases in which DNOs have addressed thee issue of a TN-S earth having become inadequate by converting it to TN-C-S. I thought that that practice,which some people here have described that as a 'lazy' or 'cheapskate', was common?

IME, I have not experienced this. One TN-S supply I visited was replaced as the lead sheath had broken down under the ground.
If that happens, you cannot trust the integrity of the other conductors, hence the cable being abandoned and replaced.

 

[JohnW2]

I have had many years of experience and the DNO have always sorted issues with their earth connections.

As I said, that has always been my I understanding. I'll leave you to argue we he who has had many years experience at the coal face.

IME, I have not experienced this. One TN-S supply I visited was replaced as the lead sheath had broken down under the ground.
If that happens, you cannot trust the integrity of the other conductors, hence the cable being abandoned and replaced.

Interesting.I thought that it was a common occurrence and,as I said,have certainly seen a good few examples myself.

Kind Regards,John