Earthing Arrangements Explained + Photo's

[Paul.M]

This is for the people still in or has just left their electrical education or for those of us that need a refresher in domestic earthing arrangements. It's all very well looking at prity diagrams in college and in books but its different when your out in the field for the first time. Hope this thread helps you and I hope that other members will post up their pictures of main incomers/earthing so others can learn and understand this subject better. I wish I could refer to something like this when I was in college.



First of all we have 3 types of earthing arrangements, TN-S, TN-C-S and TT.

TN-C-S

This is where the main earth cable from the main earth terminal (met) is connected to the neutral at the suppliers main fuse. A good way to remember the name of this arrangement is to think of the C meaning COMBINED.


TN-S

This is where the main earth cable from the met is clamped or solderd to the steel of the SWA or the led outer sheath of the incoming supply cable. Again a good way to remember this is to think that the S stands for SHEATH.

TT

The main earth cable from the met is connect to an earth electrode (aka earth rod). This is because not all properties are supplied with a TN system by the supplier so we have to insert a rod into the ground.


Notice how the earth cable on the TN systems go back to the main incomer, one goes to the main fuse (TN-C-S) and the other goes to the incoming cable (TN-S). If the main earth cable doesn't go back to the fuse or incoming cable it will be a TT. This is the simplest way I can put it without going into extended detail.



Now that we've seen some prity diagrams (am I starting to sound like a teacher lol) we will now look at real world photos that are not as straight forward as the diagrams.


First example, is it a TN-S or a TN-C-S or both?

 

[jaresquire]

PME
TNS

You decide....

View attachment 13148

Looks TN-S but the PME sticker makes me think otherwise!

 

[Silly Sausage]

Haven't read this yet, 108 pages!, but seems to have relevant info regarding this thread...

http://www.copperinfo.co.uk/earthing/downloads/pub-119-earthing-practice.pdf

 

[Air Conditioner]

Thanks for this Paul. I haven't come across a TT system on-site yet, so great to see what it looks like in reality!!


Sorry meant to quote from the TT rod photo from post 59. Still it saves a bit of space.

 

[Paul.M]

Good points E54, I also wouldn't pig tail the earth cable. Wonder how long the connection will last exposed to the elements like that?

Just a note: Never pig tail a live conductor, you've basically just made an induction coil.

 

[Silly Sausage]

Good points E54, I also wouldn't pig tail the earth cable. Wonder how long the connection will last exposed to the elements like that?

Just a note: Never pig tail a live conductor, you've basically just made an induction coil.

Coil it around the rod...can someone do the maths on that one please?!

 

[lurchio]

This has got me a bit confused, i was initially thinking TNS with the earth coming from the base of the cable but im swaying to TNCS with it running through the fuse..

 

[Richard Burns]

Very similar to the first picture on this thread.
It is possible that the earth does not join the neutral in the head but more likely a "conversion" to TNCS from TNS

 

[Chrisuk]

Hi all, since I'm only in my first year of my Level 2 C&G 2365 electrical installations it's always nice to be able to look at different set ups and recognise what they are, I saw the following and wanted to know if this one is a TN-C-S or TN-S install because I was thinking a TN-C-S but it looks like it's connected to the sheath so that makes it a TN-S install???

Thanks all

 

[telectrix]

TN=S. it's clamped to the lead sheath of the supply cable.

 

[Chrisuk]

Thanks for confirming that for me

 

[Engineer54]

Can't exactly see what type of clamp has been used in your photo, but if it's just a standard/typical pipe earth clamp, then it's not suitable for purpose, only Constant Pressure and Hepworth (think that's the name) clamps that require a tool to secure, are acceptable. 9 out of 10 TN-S cable sheath connections are made via soldered/lead wipe connections, clamps only being retrofitted as or when required!!

 

[Chrisuk]

This is why I uploaded it, I came across the picture online and had an idea but since I'm a trainee was unsure, I certainly knew i had not seen it like that before, obviously I've seen a small percentage of what's to see but this was the 1st time I've seen some sort of clamp!!

 

[telectrix]

clamps usually fitted if the soldered connection has broken off.

 

[44ALLAN]

good thread

 

[GLENNSPARK]

Hi all, since I'm only in my first year of my Level 2 C&G 2365 electrical installations it's always nice to be able to look at different set ups and recognise what they are, I saw the following and wanted to know if this one is a TN-C-S or TN-S install because I was thinking a TN-C-S but it looks like it's connected to the sheath so that makes it a TN-S install???

Thanks all
View attachment 21921

if in doubt then do a Ze...and a Zpn....if the PFC is the same then you can be pretty certain that you have a TN-C-S....
if not then its likely to be TN-S...

TT should be obvious