Noob question - What is TN-C | on ElectriciansForums

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I

Inteificio

Hi,

Such a basic bit of info, but where can I get info on a TN-C system.

Nothing in my books, and google is not my friend as everything defaults to TN-CS.

Feel embarrassed asking something so basic, but that's what forums are for =-)

This relates back to a sparky saying a dedicated CPC is not needed due to TN-C.

Don't have the info on TN-C to undestand the statement,
 
TN-C is where the neutral and the earth are combined as per TNC-S, but after the point of intake it continues to be combined. So there would be a link in all accessories between N and the earthing provision of the accessories in place of a CPC.

For this reason the use of this system is heavily restricted so much so that I have never seen one.
 
Have to remember that one MKS, assuming it is the same in the BRB (I am not green yet).

The issue being it is supposedly being used, and this is the reason cited for their being no need for a CPC on one site.

However there is a CPC on almost everything including the main distribution board.

So as a CPC is fitted to almost everything, one would assume he has converted it to TN-CS.
However on schedule of inspection it is marked TN-C with the 's' crossed out and TN-C on one of the other forms.

The is no continuity between the earth pin on two adjacent sockets, his defense is their is TN-C....
Surely if everything were combined there would be even greater reason for their to be continuity.

Moment like this I want to take the 2391!!!
 
TN-C is not used in the U.K. beyond the public distribution network - ie, not in an installation. EAWR Reg 156. Also ESQCR 2002.
 
A quick check of the BRB (could not find it before for some reason) and a chat with NIC confirmed that this is an illegal system to use in the UK for domestic...
Just when one issue is resolved another starts!
 
What exactly is this installation Inteficio? As others have said a TN-C system is heavily restricted in this country and I've never seen one either. I'm wondering if one of our eastern european cousins has been involved somewhere along the line on this one as I believe it's common practice in them there parts.
 
Trev - it's probably on a farm with some dubious SWA termination done by a family friend..................
 
Thanks.
Well a TN-C is what I thought it was. So the site wasn't TN-C even though the spark says it is...

Thanks to the links I did finally find out some info about IT too. Again one of those irritating things to search for.
I was set a task at college to find out about IT, did my research but came back with questions and teacher didn't know the answers. Why would they set a problem they don't know the answer too?

Tony does this sound like I have understood IT?

Say we have a E fault on L1. L2/N L3/N jump to 400v. L1 dumps current through a high resistance path to CPC. Touch voltage on item where fault occurred is there, but low enough that a lethal current cannot flow.
insulation resistance checker reports fault so supply can be isolated and repaired before second fault occurs.

Advantages, supply does not trip under fault conditions and semi-safe
Disadvantage - serious over voltage and just seems dodgy getting all those parallel resistance equations to get below 30mA. Then again it is not often I am sitting in a metal bath of salt water when working live so I am not the easiest earthing point.

Think I am overlooking something, anything to add?
 
IT systems there is no reference to earth so yes if you get an earth fault on say L1:
L2 and L3 become 400V with reference to earth.
Normally a DC reference current is injected in to the system which is referenced to earth. The only IT systems I’ve worked on were 660V single phase @4000A so if we did get a bang, it was quite spectacular.
This shows a earth leakage system I designed a good few years back.

View attachment 12789
 

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