tt system

[steve.t.]

hi
doing an extention of a tt system via a henely block, 50a fused switch, 16mm cable into a seperate cu. i want to discriminate between rcd's and cu's.
my question is do i connect the earth from the 16mm cable into a m.e.t then to earth rod, or just connect it to the fused switch or into the earth terminal in the 1st cu then to earth rod
any help would be great

 

[Deleted member 26818]

What kind of cable is it?

 

[steve.t.]

16mm t and e

 

[Deleted member 26818]

I think I would ditch the earth from the T&E, and run a separate conductor from the eath bar in your new CU, to the MET.

 

[steve.t.]

yes i was thinking that, would 10mm to MET be ok then 16mm out to earth rod, thanks for u're help

 

[Deleted member 26818]

It's unlikely that you will require such large conductors. What is your Ra/Ze?

 

[steve.t.]

cant do Ra or Ze yet, the building has a plastic water pipe being used as the earth electrode so i didnt even bother testing it, might do tomorrow just for a laugh, it's diabolicle. the building is not in use

 

[Engineer54]

cant do Ra or Ze yet, the building has a plastic water pipe being used as the earth electrode so i didnt even bother testing it, might do tomorrow just for a laugh, it's diabolicle. the building is not in use

So your going to use an out buildings earth rod, as the sole TT earthing source for the main building?? So what size and what length is this sole earth rod going to be??

 

[Deleted member 26818]

So your going to use an out buildings earth rod, as the sole TT earthing source for the main building?? So what size and what length is this sole earth rod going to be??

How have you determined that?

 

[Engineer54]

Basically by the O/P statement of ....''doing an extention of a tt system via a henely block, 50a fused switch, 16mm cable into a seperate cu. i want to discriminate between rcd's and cu's.''

And his further comment statement, ... ''cant do Ra or Ze yet, the building has a plastic water pipe being used as the earth electrode so i didn't even bother testing it''

So as far as i can see, the only earth rod for this installation is the extension of a non-existent TT system. Did i miss read something or other??

 

[malcolmsanford]

hi
doing an extention of a tt system via a henely block, 50a fused switch, 16mm cable into a seperate cu. i want to discriminate between rcd's and cu's.
Are you sure the Zs for that 16mm cable will be low enough on a TT system to activate this Fuse?
my question is do i connect the earth from the 16mm cable into a m.e.t then to earth rod, or just connect it to the fused switch or into the earth terminal in the 1st cu then to earth rod
any help would be great
You have to have in your Installation a MET Reg 542.4.1 whether that is a seperate block or the Earth bar in the CU and your main earthing conductor from your rog goes into this Block/CU bar and then your CPCs

For the post 5 look at regulation 543.1.1 and you can see that there may not be the need for such a loarge main earthing conductor

 

[steve.t.]

the building is 3 very small seperate units, and what someone has tried to do is turn it into a tt. it has an overhead cable coming in from a seperate building. so what i'm doing is making sure it is all earthed properly and not just the single unit that will be in use, but i have to split the tails into a henely and take it into a seperate cu, so shall i put a MET in and earth everyting back to that, i was just confused about what to do about the earth from the 16mm cable from the henely into seperate cu