TT system

[Engineer54]

On second thoughts though, is it not possible to use the combined csa of you armour and 3rd core as a bonding earthing conductor? thus continuing the PME, I don't like the sound of your soil conditions and would not personally leave it as a TT with those readings! Look at it now its wet! what will it be like in next summers inevitable 'heatwave'?

50 M isn't that far for a 16mm cable. use the 3rd core as your bonding conductor and the armour as the CPC.
What your talking about, would only affect a situation where the 3rd core wasn't of a suitable size to fulfil bonding CSA requirements, and then relying on the armouring to make-up the shortfall!! Not the case here, looking at it only at face value that is... lol!!!

 

[rich.250]

what the hell does that mean...

""Tncs, but is it PME???""

same bloody thing with a different name!

Not necessarily. Protective multiple earthing is earthed at multiple points on the way back the the transformer....
As where tncs isn't!

It was meant as a joke..... Sorry

 

[JD6400]

Take an Ra reading off the metal frame of the building. If it's got good foundations - might just do.

Although I totally agree with you and personally see it as the best possible means of gaining a very respectable Ra .

However after a discussion with another contractor on the subject about 2 months ago , we enquired with the ECA technical about if it was permissible to use a steel framed building as essentially a means of a main earth and were unequivocally told no !
So i would imagine the same rule would apply to using the frame as a means of helping to lower the Ra to a more acceptable level !?

 

[RogertheBodger]

Although I totally agree with you and personally see it as the best possible means of gaining a very respectable Ra .

However after a discussion with another contractor on the subject about 2 months ago , we enquired with the ECA technical about if it was permissible to use a steel framed building as essentially a means of a main earth and were unequivocally told no !
So i would imagine the same rule would apply to using the frame as a means of helping to lower the Ra to a more acceptable level !?

Interesting ...... Can't think of a reason why they would say that, unless the building you were discussing already had a pme or multiple pme supplies, or something along those lines.

Surely the connection to earth under a building with driven piles and/or sitting on a reinforced concrete slab would be better than an earth rod that can only be driven half a meter into the ground.

 

[JD6400]

No it was a cattle barn in the middle of others and all TT , I can not for the life of me see why it would be unacceptable but he was adamant about it , i think he may have even quoted some reg numbers as well , but alas my memory is about stuffed nowadays !

But then as a thread from a few months ago in which i think Lenny or Engineer54 pointed out , you are allowed to use structural steels as a main bonding conductor to say your gas or water at the other end of a building , but not as a main earth ?

 

[RogertheBodger]

No it was a cattle barn in the middle of others and all TT , I can not for the life of me see why it would be unacceptable but he was adamant about it , i think he may have even quoted some reg numbers as well , but alas my memory is about stuffed nowadays !

But then as a thread from a few months ago in which i think Lenny or Engineer54 pointed out , you are allowed to use structural steels as a main bonding conductor to say your gas or water at the other end of a building , but not as a main earth ?

Even stranger then.

Structural steel is OK to use as a main bonding conductor, although I think they were talking about buildings that already had a TN supply, but in this case the Bonding/Main earthing conductor would be combined. I wouldn't have a problem using the building as a TT earth if it was possible to get a better Ra value than the rod.

Perhaps your man at the ECA was having an off day, don't we all lol.

 

[Engineer54]

No it was a cattle barn in the middle of others and all TT , I can not for the life of me see why it would be unacceptable but he was adamant about it , i think he may have even quoted some reg numbers as well , but alas my memory is about stuffed nowadays !

But then as a thread from a few months ago in which i think Lenny or Engineer54 pointed out , you are allowed to use structural steels as a main bonding conductor to say your gas or water at the other end of a building , but not as a main earth ?

Depends whether the steels have been driven into the earth, or are connected to a Ufer earth, whether it will be a good earth or not. You need to check/test first...

Other than that i'm afraid your man from the ECA is talking out of his rear end, as to not being able to use such a system as your TT earthing !! ...lol!!!