TN-C-S to TN-S !!!

21 May 2011
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West Midlands
United Kingdom
I'm scraching my head with this one...! Street lighting circuits, the supply comes in as TN-C-S Board supply, gose to a small two way circuit board which has a single pole and nuetral and two HRC fuse outputs. 1 which goes up to the lamp column, the other goes to another colume with a simla fuse protection via a swa cable. Now here is the Question ! I'm shown by the company spark the way they do there Test Sheets, Sheet One you wright the incoming supply which is TN-C-S for the first colume.
And on Sheet Two Underground Cables, you wright the incoming supply as TN-S I thought if it comes in as TN-C-S it stays as tn-c-s maybe i need to go back to collage.!! :mrgreen:
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Without looking anything up, I would think that's reasonable, as I presume the second column is fed by a separate neutral/separate earth.
Without looking anything up, I would think that's reasonable, as I presume the second column is fed by a separate neutral/separate earth.
It's really a 'bureacratic question', but I thought the whole point (definition) of a TN-C-S supply was that it starts out with neutral and PE combined and then, at some point (usually entry to a building for indoor installations), they separate (hence "-C-S"). That doesn't stop one calling the 'installation' a TN-C-S one throughout, even though the neutral and PE remain separate throughout the actual interesting.

I guess the underlying bureaucratic question relates to what is considered to be 'an installation' when one is talking about street lighting!

Kind REgards, John
From memory we are not allowed to install a combined neutral/earth cable into a street lamp.
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I'm sure I've worked on Leeds city council streetlighs with a PME feeder. It's a few years ago now, so I might be wrong.
I've worked on lots of PME fed street lighting columns. Even had one with a broken PEN conductor over christmas......
Oh I know there are a lot of PME fed columns but ......................
(I'll have a read through the relevant documents on Monday)
now here is my input as someone whom works on streetlighting currently as a sparky!

most newly installed columns with a DNO Supply, have TNCS Earting Arrangement, on the test sheets any colums that are supplied from a private network say outgoing ccts in a feeder pillar are noted down as being a TNS service even if the DNO Supply to a feeder pillar is in fact a TNCS.
hi don't no if i can be any help to any of these threads but im a electrician with 20 years experience now working as a overhead lines man for the last 2 years and would just like to state that there is no such a thing as a tns system at some point in the line they are combined as earth is neutral be it at the substation or at the nearest transformer neutral originates from the ground
Maybe you ought to do a bit of reading up on electrical supplies and earthing systems... :eek:
Yep, if the supply is TN-CS then you cannot have a directly connected system becoming TN-S downstream, it is still TN-CS.

Always made me wonder though if the DNO ever gives us what is TN-CS upstream in a split concentric or PILC, making the normal sparky think it is TN-S

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