TN-C-S Confirmation

[stuban]

Hi,

[introduction in new members section]

We have a CU to fit to replace a re-wireable fuse board. The incomers are pretty new and look to have been fitted fairly recently. However it looks like a tn-c-s with one major missing factor... No earth block from the incoming Neutral. There's no earth stake so it's not a TT. There seem to be CPC's connected to the terminal in the fuse board but there's not actual earth to the block.

In your experience what's the best way to proceed? We've contacted the board and booked in a visit(next week!) for them to check it out and tell us if it's set up for tn-c-s or whether we need to put a stake in for TT.

In you chaps experience is there any way that we could confirm(either way) this by testing or is this the only way to go?
Could we equally just use it as a TT(assuming the Ze was OK)?

Thanks in advance
Stu

 

[Deleted member 9648]

I would prefer a TNCS to a TT all day, you cant test to verify TNCS is present...despite some on here who will state that you can. Only the DNO can verify that, and as you have them coming next week I would wait till then.

 

[IQ Electrical]

If you report 'an installation with no means of earthing' rather than asking for confirmation of the system type, you often get a visit within a few hours.

 

[stuban]

So worth putting the call in and waiting rather than forging ahead with a TT.

Thanks chaps

 

[nickblake]

It wouldnt be a TNS would it but the wire from the sleeve is hidden , have you done a Ze on it , the Ze for TT should be less tha 200 ohms TNS 0.8 and TNCS 0.35 , with the installation earths connected there could be a possibilty of a parralle earth path , agree with wire puller and IQ on this one , TT is a last resort for me unless required to do so

 

[stuban]

It could possibly be but I saw no cable over 4mm in the earth term inside the board(assumed this was part of the 4mm t/e to the kitchen)

We didn't have the meter with us at the time for various reasons so haven't done a Ze yet. With no earth incoming where would we run the test though?(bear in mind this is all theoretical now because we've got the supplier coming but I would like to know if we're missing a trick)

Cheers
Stu