What size earth on a TT ?

[JD6400]

What do others think of this one !?

On one of our last scam visits , we got talking about TT and he came out with the need to install 16mm from the rod !?
16mm ! I query ?
Yep look in you on site guide , he says !

I have since phoned the technical help line on another matter and also raised this point , and was then told to ignore the on site guide and go with 10mm no matter what it is run in !:juggle2:

I just love how the left hand has no clue what the right hand is doing and neither are listening to the master or his mouth !

 

[trev]

Funny that. I could have sworn there was a calculation we were supposed to do to size the earthing conductor.
Maybe it's in the new amendment that we can just blindly chuck a 16 in

 

[telectrix]

as trev says. ^^^^. 16mm only if buried without mech. protection.

 

[Engineer54]

It's a shame the IET don't better describe the requirements of the electrode these earth conductors are being actually connected too, it'd make much more sense then!! In fact the whole section covering TT system earthing, needs a complete revamp!! ....But no, instead they arse around with CU enclosures, and readjusting max Zs values, neither of which needed tinkering with in the first place!!

 

[JD6400]

The trouble is , the assessor has the potential to cause us a lot of hassle if he chooses to !

This is the same scam provider that had one eyed Robin on their books ( I am sure some will know him ! ) , he got very iffy with us one year whilst on a site visit after he noticed that we had stopped installing flying earth leads to back boxes , even though I could name the scheme staff member who had advised us not to , only the month before !

Then on the next inspection he got shirty because we did not have a copy of the em lighting regs , or the likes ? And then sold us a burnt copy of these and other bits , so that we could "pass" our inspection .
I subsequently found out the following year that he had been caught and asked to leave , but only after netting a estimated 30-50 k , apparently our £180 cash was over the odds compared to most !

Then they wonder why we hold the """"s in such contempt

 

[TJ Anderson]

The trouble is , the assessor has the potential to cause us a lot of hassle if he chooses to !

This is the same scam provider that had one eyed Robin on their books ( I am sure some will know him ! ) , he got very iffy with us one year whilst on a site visit after he noticed that we had stopped installing flying earth leads to back boxes , even though I could name the scheme staff member who had advised us not to , only the month before !

Then on the next inspection he got shirty because we did not have a copy of the em lighting regs , or the likes ? And then sold us a burnt copy of these and other bits , so that we could "pass" our inspection .
I subsequently found out the following year that he had been caught and asked to leave , but only after netting a estimated 30-50 k , apparently our £180 cash was over the odds compared to most !

Then they wonder why we hold the """"s in such contempt

He would not get along well with me. I allow three hours out of my day for my CPS assessment and I provide a local job to look at. All Paperwork out and ready. I Will be having my 10th one this year. If there was any personal preference nonsense (outside BS7671)from him I would end the visit right there and switch CPS. All they are to me is a vehicle to enable me to notify jobs, nothing more.

 

[spark 68]

If I knew I was correct then I would argue the ---- and I would get him to show me in the regs book/GN where I had not complied.

Obviously we don't want to cause un-necessary grief for ourselves on assessments, but if pushed and I knew I could back myself up then I would make a stand.

Fortunately my assessor is/was a proper spark and knows his stuff, besides he knows that I also know my stuff, so I have had no problems in the 5 or 6 assessments I have had so far, in fact he once suggested an easier way I could have complied with the regs in a bathroom one time.

Maybe some of the newer entrants to our trade are a bit in awe of these assessors, I just treat them as I would another spark, if they took the p!ss then they would be told in very short order, besides I am paying them and technically they work for me lol

 

[Octopus]

It's a shame the IET don't better describe the requirements of the electrode these earth conductors are being actually connected too, it'd make much more sense then!! In fact the whole section covering TT system earthing, needs a complete revamp!! ....But no, instead they arse around with CU enclosures, and readjusting max Zs values, neither of which needed tinkering with in the first place!!

Hit, nail and head spring to mind.

 

[JD6400]

He would not get along well with me. I allow three hours out of my day for my CPS assessment and I provide a local job to look at. All Paperwork out and ready. I Will be having my 10th one this year. If there was any personal preference nonsense (outside BS7671)from him I would end the visit right there and switch CPS. All they are to me is a vehicle to enable me to notify jobs, nothing more.

I do not blame you either !
This was 5 or 6 years ago now , and to be honest their appearance more bemuses me than anything else now days , but we still try to look like we are jumping through the hoops , for a easy life if nothing else !

I remember our first assessor ( 10 years ago ) , he had been a kitchen fitter 3 weeks before , and had never even see a proving unit and was well impressed that they existed , to the point of taking pictures of it so that he could show the other assessors what it was .

 

[Deleted member 26818]

I don't understand why anyone would suggest either 16mm or 10mm?
I believe the minimum CSA from memory, is 4mm.

 

[Octopus]

I don't understand why anyone would suggest either 16mm or 10mm?
I believe the minimum CSA from memory, is 4mm.

The higher CSA's are due to the lack of mechanical protection. Don't have my regs or ISG to hand but thats what I recall!

 

[123]

It's 2.5mm IIRC

 

[Deleted member 26818]

Surely these people at the help desks would be able to inform someone of which CSA is required for various situations?
My understanding, is that the minimum CSA of a sheathed earth conductor with mechanical protection is 2.5mm, irrespective of whether it is buried in the ground or not.
Where there is no mechanical protection then the minimum CSA is 4mm, unless buried in the ground where the minimum is 16mm.
The minimum CSA for bonding and main earth conductors where PME conditions apply is 10mm, which would not be applicable for a TT installation.
Then of course there are other minimum CSAs for steel and aliminium conductors, which unfortunately I can't recall.

 

[123]

Better than my answer. I don't think there a size for Aluminium, only copper and steel. My BGB is upstairs though and I ain't moving to get it.

50mm2 rings a bell for unsheathed steel

 

[TJ Anderson]

Minimum CSA of Buried Earthing Conductor:
Protected against mechanical damage and against corrosion by a sheath - 2.5mm copper or 10mm steel.
Not protected against mechanical damage but protected against corrosion by a sheath - 16mm copper or 16mm coated steel.
Not protected against corrosion and irrespective of protection or not from mechanical damage - 25mm Copper or 50mm Steel.