TNCS earthing arrangent

[chrisreid186]

hi guys just a question on tncs

TNCS has a combined earth / neutral

am i right in saying If the neutral failed then the whole installation would become live and you would also loose the earth, however if you bonded the incoming services (water/gas) would this become the fault path? through the met, down the bonded pipework, through general mass of earth and back to the transformer like a tt system ??

 

[pushrod]

Yes if the neutral was lost you also lose the earth.
If there is a line fault to earth and the resistance through the pipe work is less than 1667 ohms then any 30 mA rcd will still trip.

 

[roukel01]

Depends where the neutral is lost. PME = Multiple earthing.. ie lots of earth rods along its path. Infact on the new installs I have seen (industrial) they always plonk a rod in whilst they are onsite. and so even if the neutral failed just outside, you still have an earth path