T-NS or TN-C-S service head ?

[Traineeboy]

Hey chaps just wondered if I could get some clarification. I understand the difference between earthing arrangements. I know TN-S the earth is sheath of the cable and TN-C-S the earth is combined with the Neutral, PEN conductor. 

Whenever I go on a job I normally know what type of earthing system we are working with. We went to a job the other day  where the customer had a new supply put in. The service head states it's a TN-S (SNE) but it looks like a TN-C-S as you connect the earth to service head rather than it coming from a clamp from the sheath of the cable. The property is out in the sticks.

It also has a note on it staying DO NOT connect to the earthing terminal ! There for I’m puzzled. Here is a picture of the service head. Peoples thoughts ? 

 

[Sharpend]

The pic is too close to see anything? Cant see what you are referring too? 

 

[Traineeboy]

The pic is too close to see anything? Cant see what you are referring too? 

Fair point 

 

[Traineeboy]

 

[Sharpend]

Ok so does the installation comply for a TNS earth arrangement? 

 

[Fleeting]

It is TN-S, SN/E means Separate Neutral/Earth supplied through a split concentric cable there is no PEN.

 

[Traineeboy]

Yes it does comply. I was just a little confused as it is unlike the normal domestic service heads ( TN-S) I see the earth supplied by the sheath not connecting into the head it’s self. But Fleeting thank you for highlighting split concentric cable, that’s probably why. Thanks for you input and don’t like to appear that I don’t know what I’m talking about but just like clarification  The chap my boss has placed me with is a Wally and don’t bother asking him questions lol It’s the first time I have seen this type of service head as I normally go to jobs and it’s always an old service head, never a brand new one so it just threw me. Thanks 

 

[Murdoch]

Imho that's a new supply for a building site so it has to be TT until it's complete

 

[Traineeboy]

Imho that's a new supply for a building site so it has to be TT until it's complete

It’s not a building site it is a domestic property estate. WPD put in a 3 phase but customer is only using one of the phases for now. He is using the phase to power his new big out building which is completed it just needs to be connected to the new supply. But yes it is uncommon. 

 

[Fleeting]

One of two things are going on in the service head either the neutral and earth are kept separate or they are combined at one terminal (CNE). You need the supplier to connect the earth.

 

[Murdoch]

It’s not a building site it is a domestic property estate. WPD put in a 3 phase but customer is only using one of the phases for now. He is using the phase to power his new big out building which is completed it just needs to be connected to the new supply. But yes it is uncommon. 

Interesting answer as nothing is connected ....... and hence my original answer

 

[binky]

I think the earth terminal cover can be opened on those without cutting seals, so you could open it up and test for Ze to see if there is an earth connection. 

 

[Fleeting]

I think the earth terminal cover can be opened on those without cutting seals, so you could open it up and test for Ze to see if there is an earth connection. 

Not sure we should be advising someone to interfere with the service head aside from him being a trainee it is illegal.

 

[Sharpend]

I think you’ll find we are permitted to connect to those earth terminals on the service head. 
I have certainly done this over the years with industry acceptance? 

 

[binky]

Not sure we should be advising someone to interfere with the service head aside from him being a trainee it is illegal.

 if the earth teminal plate has been designed to be accessible, then it's not interfering. 

 

[Fleeting]

 if the earth teminal plate has been designed to be accessible, then it's not interfering. 

I am not familiar with the Series 8 service head but many will need the right side fuse carrier removing to remove the cover. In any case below that cover you will either have a CNE terminal or separate neutral and earth terminals, in both cases the CNE and neutral terminals will be deemed live parts it is not for us to interfere with them.

 

[binky]

I am not familiar with the Series 8 service head but many will need the right side fuse carrier removing to remove the cover. In any case below that cover you will either have a CNE terminal or separate neutral and earth terminals, in both cases the CNE and neutral terminals will be deemed live parts it is not for us to interfere with them.

they are designed so that you don't do anything with the fuse carrier. As for live terminals, we deal with those every day in Consumer Units. 

 

[Fleeting]

they are designed so that you don't do anything with the fuse carrier. As for live terminals, we deal with those every day in Consumer Units. 

I don't think you can compare the two as you have no opportunity to carry out safe isolation on a service head. 

 

[binky]

I don't think you can compare the two as you have no opportunity to carry out safe isolation on a service head. 

the point I'm making is that if you cant firk with live leccy safely, you shouldn't be a sparky, and  that's a neutral / earth terminal not line, so last time I was in a CU and touched the exposed neutral bar 'nothing happened' . Now I'm not suggesting sticking fingers in places they don't belong, but, a test probe isn't an issue in circumstances that are low risk, hence it has the removable cover that doesn't require the seal fairy. 

 

[Fleeting]

the point I'm making is that if you cant firk with live leccy safely, you shouldn't be a sparky, and  that's a neutral / earth terminal not line, so last time I was in a CU and touched the exposed neutral bar 'nothing happened' . Now I'm not suggesting sticking fingers in places they don't belong, but, a test probe isn't an issue in circumstances that are low risk, hence it has the removable cover that doesn't require the seal fairy. 

The neutral is deemed a live conductor and you need to remember your suggestions are being aimed at a trainee not a seasoned "nothing is going to happen to me" electrician.