requirements for tt earthing?

[thekingiam]

was looking at a tt cu and the main earth goes outside into a concrete driveway cable looks quite small, is the minimum cable size requirement the same as other earthing arangements?
if i do need to replace, would i need to provide inspection pit.
its being protected by a rcd,could i use rcd as means of isolation while changing cu?.
testing earthing arangement could i do earh loop test on my multimeter instead of having to buy electrode tester?

 

[Guitarist]

Here we go again, lol.
Page 41 of the Green OSG table 4.4(ii)
2.5mm min size when protected against corrosion and mechanical damage, ie sheathed and in conduit, buried or not buried.

The figure in dispute is the 4mm for not buried but protected/not protected against corrosion. Clearly stated in the OSG but no reference to it in the regs...

 

[Engineer54]

but my argument was why the hell does the pic in the OSG show 16mm CSA.....as if that CSA will make much difference to a TT earthing arrangement...lol....

Depends doesn't it, ...if were talking about the numbty 200 ohms as mentioned in BS7671 then your probably correct...lol!! But if you (god forbid) managed to install a decent TT system and got the Ra down to 1 ohm or even sub ohm value, then a 10/16mm earthing conductor from the earth electrode(s) would be quite prudent!! lol!!

 

[huntos33]

If your running out a sub main to a garage on a TT system is there any issues with spiking the board in the garage as well as the main spike at source ?

 

[Engineer54]

If your running out a sub main to a garage on a TT system is there any issues with spiking the board in the garage as well as the main spike at source ?

None whatsoever, in fact it would be prudent to do so!! The more earth rods or positions on a TT system the better!!

Link the 2 earth rod positions either using the SWA of your sub-main cable, or by a separate conductor to the MET via the EMT of your garage CU....