Question regarding old steel TN Earthing conductor from supply sheath

[ZEDEZ]

I'm a little confused as to where the responsibility lies for the conductor described in the title. You know the type - on old TN supplies where you've got a bare multistrand conductor coming from the sheath to the M.E.T that's always of a fairly piddly CSA.

My understanding is that this is the responsibility of the DNO, and as long as there's no sign of thermal damage and it tests OK, then there's no issue.

Hoping someone else can shed a little light on this, thanks.

 

[telectrix]

agree with your observation except that it may be tinned copper and not steel. as long as it can handle the fault current for the duration necessary, then it's fine for continued use.

 

[davesparks]

You need to calculate the required size using the adiabatic equation to establish whether or not it is suitable.

Checking for signs of thermal damage is more about assessing undersized bonding. An undersized earthing conductor is more likely to melt away when it is required than just show signs of overheating

 

[telectrix]

You need to calculate the required size using the adiabatic equation to establish whether or not it is suitable.

Checking for signs of thermal damage is more about assessing undersized bonding. An undersized earthing conductor is more likely to melt away when it is required than just show signs of overheating

so if it's been there for 50 years and has not melted. there's a fair chance that it's OK?

 

[Midwest]

Why don't you ask the DNO to have a look if it's a bit manky, seeing's though your not supposed to touch their clamp/equipment?

 

[ZEDEZ]

agree with your observation except that it may be tinned copper and not steel. as long as it can handle the fault current for the duration necessary, then it's fine for continued use.

Looking at the Zs and cut out fuse type, and assuming it's tinned copper (which I'll have to double check) if I run the adiabatic equation on it I'm getting a minimum CSA of 2.14mm2.

Interesting!

That answers my question then

 

[ZEDEZ]

so if it's been there for 50 years and has not melted. there's a fair chance that it's OK?

I think what Dave means is that, at a glance, if you saw thermal damage, that would instantly indicate to you that you had an undersized Earthing conductor.

But to really know the required size, you'd have to run the adiabatic equation ... Which I did just now, and got a result of 2.14 mm2

It's all making sense now

 

[davesparks]

so if it's been there for 50 years and has not melted. there's a fair chance that it's OK?

Nope, if it's been there 50 years and not melted it either has not suffered an earth fault of significant size or it's the right size or the bonding is linking everybody in the street together via a common metallic service

 

[7029 dave]

IMO if its a tns band, then It's the DNO's baby.Give them a call if you have concerns.

 

[Davisonp]

as long as there's no sign of thermal damage and it tests OK, then there's no issue.

I was told the same thing by my ELECSA inspector a couple of years ago.

 

[davesparks]

I was told the same thing by my ELECSA inspector a couple of years ago.

Whoop de doo! I had an elecsa inspector who refused to accept my strict compliance with the letter of bs7671 and wanted me to comply with his preference instead, he also missed an extraneous conductive part I had deliberately disconnected the main bonding from just to see if he knew his stuff. Needless to say elecsa received a written complaint and they did precisely nothing to deal with the bloke.

The final conclusion: Elecsa inspectors aren't worth their weight in pigeon ****!

 

[Midwest]

Whoop de doo! I had an elecsa inspector who refused to accept my strict compliance with the letter of bs7671 and wanted me to comply with his preference instead, he also missed an extraneous conductive part I had deliberately disconnected the main bonding from just to see if he knew his stuff. Needless to say elecsa received a written complaint and they did precisely nothing to deal with the bloke.

The final conclusion: Elecsa inspectors aren't worth their weight in pigeon ****!

Whilst I agree with you for disagreeing with the previous post, I do disagree with your last sentence.

With all my dealings with the assessors in person and the technical line, I've found them to be very knowledgeable, certainly know more than me, but some might say that's not hard. I can't comment on your assessment you set up, but known of us are perfect and we all make mistakes.

My beef with them is the cost of their service, the assessment process itself & frequency. Can't fault their credentials IMO.

 

[telectrix]

there's good and bad apples in every barrel.