tt Certification

[stidge]

some help please on my 1st tt installation.i am rewiring a property and was wondering about the certs.when i am filling in measured ZE on some ccts they may be higher than the Max ZE,do i just fill in as usual?comments box? advice muchly appreciated.

 

[telectrix]

you mean Zs, surely. you should enter the measured Zs readings on your schedule. for the max. allowed you can enter 1667ohms. assuming that all circuits are RCD protected ( 30mA)

 

[Octopus]

Just because you can enter 1667 ohms doesn't really mean this is OK. Your Ze must be less than 200 ohms - much lower preferably

 

[vitoboy]

ive got a job on at the mo that ive put a new earth stake in...the dno refused to connect pme even though its there on the grounds that its unreliable.
so my ze is now 475 ohms..
ive put in another stake on the end of a bit of 10mm and put it in the ground up to 10m away from the other stake(both connected at same time)
and i still get 370 ohms
if i run water in the stake hole i get 300.......for about half hour...then 370 again.
its an on going thing where i live its a mining area and all is made up ground.
any ideas...
ps ..i need to use this job for my yearly nic inspection.will they accept that its as good as it can get or need me to bury a big lump of metal to try and comply to 200 ohms??????

ta
vitoboy

 

[IQ Electrical]

The 200 Ohms figure is a rough guide to allow for degradation of the contact on the electrode due to freezing and drying of the soil.

Depth is absolute key here-an electrode 2 metres deep with an Ra of 400 Ohms will be far more stable than an electrode 1 metre deep with an Ra of 200 Ohms.