Tnc-s query

[Sav]

Hi everybody,

Hope your having a good weekend so far.
Just a quick question and if some can clarify the following.

I read that any EXTRANEOUS conductive parts should be connected to the M.E.T at the supply intake and not the earth bar in the consumer unit.

Fair enough, BUT if there was a neutral fault and the earth became a conductor, surely then as there would be a link from the M.E.T to the consumer units earth bar, everything would become live.

So why not put the extraneous conductive parts in the consumer unit ??

Hope someone can clarify this , as I am trying to find an answer !!!

Best regards to you all,

Sav

 

[Deleted member 9648]

I assume you are refering to extraneous conductive parts in an outbuilding where on a tncs they must be main bonded back to the MET rather than the local consumer unit.
Regardless of where it all runs to all extraneous and conductive parts will be at the same potential in the event of a fault....they are all joined together whether connected to the MET or the CU.

 

[Spudnik]

I have never worried about going back to the CU rather than an MET.

As far as i was aware, the only reason for using an MET was to aid testing.

 

[nickblake]

TNCS amazing how many places you cant use TNCS caravans etc ,i do agree because you bond every thing if you loose the suppliers neutral it backfeeds down the eartth and makes every piece of bonded metal live,may not happen very often with underground supplies but it does all the time with over heads been called to loads of installs where every thing was live ,fun when its three phases all bonded was live job to get cover of dist board had to use my insulated gloves pulled the fuses still live it was wirard had a job in an office block supply lost its neutarl in a gale exploding HF Balasts flickering lights it was mad all caused by a lost neutral , found 110 volts on the earth and 400 volts accross the fittings it was back feeding down the neutral bar as it had no where to go and back up the other phases ,replaced loads of hfs blew tills computors it was a right mess