TT main earth

[Jc1996]

If you have a TT island does the earthing conductor have to be 10mm or 16mm if unprotected? I know it can be 2.5 if mechanically protected and protected against corrosion.

 

[binky]

If you have a TT island does the earthing conductor have to be 10mm or 16mm if unprotected? I know it can be 2.5 if mechanically protected and protected against corrosion.

Minimum earth size 6mm, but have forgotten why . 10 is probably fine on a TT, you could confirm that via the adiabatic equation, something else I've forgotten how to use, old age and daftness are setting in

 

[steptoe]

I could do a BorisJ and be pedantic and tell you it's not a main earth, and then not answer the actual question.

In reality, a 10mm should be fine, if you are in doubt calculate it, but I've not yet come across a normal domestic that has required anything larger than 10mm on a TT system.

Why wouldn't you protect it tho, a bit of PVC conduit isn't going to take the profit from the job.

 

[NozSpark]

IIRC when I did a recent course this kind of question was asked.... clipped direct needs minimum of 16mm as the sheath isn't classed as mechanical protection

 

[binky]

IIRC when I did a recent course this kind of question was asked.... clipped direct needs minimum of 16mm as the sheath isn't classed as mechanical protection

I'm fairly sure it used to be 6mm unprotected, trouble is you get idiots come in behind you and tell the customer it has to be 16mm because they don't understand TT. So in some ways installing 16mm is better for the customer, not that it should be like that.

 

[Fleeting]

It should be selected in accordance with Regulation 543.1.3 or 543.1.4.
Where the conductor is to be buried use Table 54.1.

 

[Mike.J]

Yes we all use the adiabatic equations and reference books when out on site, just fit 16mm and move on.

 

[Jc1996]

one job I’ll have to go back to. I though it was 10mm

 

[Jc1996]

I’ve done myself dirty only conduit I had

 

[Andy™]

one job I’ll have to go back to. I though it was 10mm

you never said if its buried or not. if buried then 16mm copper if sheathed by table 54.1. otherwise adiabatic... and for an earth rod, fault current isnt going to be enough to melt a 10mm... you could easily use less if you wanted

 

[Andy™]

IIRC when I did a recent course this kind of question was asked.... clipped direct needs minimum of 16mm as the sheath isn't classed as mechanical protection

if its buried, it does need to be 16mm if not mechanically protected... but if its buried its also not going to be clipped direct. so you then have 543.1.1 which states min 4mm if not protected against mechanical damage

 

[Fleeting]

Wet string nine times out of ten all it does is earth the electrode.