Mains earthing terminal and other earthing issues!

[Danielwareham]

I'm changing my CU for my elecsa assessment and need some pointers on earthing. I have a TN-C-S system that feeds my main CU and a second CU that supplies an extension. My main concerns being there are two earths from the distributors supply (see photo below) one running directly to the CU earthing terminal and the other to the gas supply. The bonding from the water runs directly to the CU earthing terminal. Another problem is the earth from the supply to the second CU is not long enough to reach the earthing terminal in the new main CU as before (see photo). When I add the main earthing terminal this should solve some problems with the suppliers earth connecting directly to it and with 10mm running from the gas and water to it also. What about the earth from the second CU supply that on the existing setup connected to the the main CU earthing terminal? Would it now connect to the MET, is that right? Can it be extened if it's not long enough and how? And the second earth from the supplier would it go to the MET? Finally from the MET a 16mm earth to CU earthing terminal? Looked straight forward in OSG and part P green guidance book but the second CU and two earth wires from supplier have thrown me

 

[Sintra]

As you say run a 16mm from cut out and install MET. From the MET connect both gas and water protectve bonding conductors and cpc to cu 1.

If cu 2 is a sub main from cu 1 then leave the cpc for cu 2 in cu 1.

If cu 2 is a sub main from a set of split tails then connect the cpc to the MET.

If the cpc for cu 2 needs to be extended then this can be crimped and heat shrinked.

 

[Danielwareham]

Thanks... That's was amazingly helpful. CU 2 is a sub main from a set of split tails so I would be connecting the cpc to MET. Just to be sure both cpc's from cut out connect to the MET with a 16mm cpc connecting to CU earthing terminal?

 

[Sintra]

You only need one 16mm from cut out to MET and yes 16mm to cu earth bar

 

[Danielwareham]

I thought that's what you might of meant from your first post. Everything else I'm clear on. It's just that I'm a little nervous about going near the cut out. Not too sure on the process on removing the cpc. I thought the cut out was something you pretty much left alone other than removing the main fuse to kill the supply. Why does it have two cpc's running from the cut out anyway? I guess it would be ok to keep the two cpc's and connect them both to the MET?

 

[malcolmsanford]

As you know your TNC-S system will have a link at your cut out between Neutral and Earth. If you opened the cut out you would see the link, it would be in a small ,well MET really, of perhaps 3 terminals.

It is quite simple really to just remove those 2 earths and run a 16mm as Sintra said to a new MET where you would then take your bonding and CPC to CU from. As you know your not really suppose to do anything to a cut out, even remove the fuse, though some DNO's have issued statements allowing scheme members to do this under certain conditions ie that the meter or head are not damaged or have signs of being tampered.

Personally I would remove the 2 earths and run a 16mm, Elecsa are pretty good and world wise, they will know you have removed the fuse and will also know that you have changed the main earth condutor to 16mm

 

[Danielwareham]

Thanks. Very helpful indeed