earthing system ??

[john1doherty]

hi all
just been out to do a minor works install today, addition to a 24v supply for magnetic door holders linked to the fire alarm panel and the boss asked me to fill in a niceic minor works ( dont think we need to be doing them for 24v ?)
went out to check the main incomer to see what type of earthing arrangement we had and was slightly confused, it was in a large nursing home and 3 phase supply but coming in with the incomer was a 16mm earth going into the supply company's spreader box with the swa, then coming out of the large terminal bar on the side was a 25mm earth connecting to the consumers earth i assumed it was a tn-c-s system but now i am having doubts, anyone got any ideas what i have here ?

cheers

 

[sparkymalarky]

This post is crying out for a photo mate.

 

[john1doherty]

wish i had taken one at the time but...........

 

[somersetsparks]

You may find it is TNCS, with an additional stake, impossible to prove without photo though! and evn with photo really, by enquiry would probably be best method.

 

[Richard Burns]

With a 16mm earth coming from the supply (assuming it does come from the supply) then you are looking at TNS but if it is joined to the neutral at the ehad then it is TNCS (with the supply sheath earthed!).
Measure PSC and PEFC if they are the same value then head for TNCS.