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?

 

[SJD]

It kind of looks like TN-C-S, plus an extra earth to the incoming cable sheath, as if the supply was once TN-S, but perhaps has been converted to TN-C-S?

 

[Paul.M]

It kind of looks like TN-C-S, plus an extra earth to the incoming cable sheath, as if the supply was once TN-S, but perhaps has been converted to TN-C-S?

Ten out of ten for SJD!

Yes its in an area where the DNO is installing TN-C-S to all the houses so at the time of the picture it was both so they could switch over without disconnecting an earth path from anyone's house. Just a good example to get the ball rolling on this thread.

 

[Paul.M]

TN-S

You can clearly see the main earth cable connected to the 'S'heath.

 

[Engineer54]

If you have a neutral connected to an installations earth terminal (eg PME/TNC-S) then the incoming supply cables metallic sheath connection must be disconnected. Especially important where a supply cable is suppling both TN-S and TNC-S earthing arrangements!! eg, ....where the DNO cable is in the process of being PME'd....

 

[Paul.M]

TN-C-S

Another obvious one, were is the earth cable going? Ho to the main fuse therefore its a TN-C-S. C = Combined.

 

[telectrix]

post deleted

 

[Paul.M]

TN-S , paul, not TNC-S.

Predicted text Tel lol. Now edited and me looking like a muppet again .


@ E54, the DNO "forgot" to come back and disconnect the TN-S. A Ze was taken on the pme to establish continuity before my snips came out. I also called the DNO to make sure, now that's twenty minutes of my life that I won't get back.

 

[telectrix]

deleted post now you've edited. i knew it was a typo. LOL.

 

[Engineer54]

Haha, ....I hope you wrapped the remaining exposed sheath in amalgamating tape, as it'll still be an extraneous earth?? lol!!

 

[sedgy34]

its got to be an old tns changed to a pme but if think there its been left like that cause of corrosion to there incoming cable
i remember something the DNO mentioned to me a few months back regarding an installation query i had

 

[Engineer54]

its got to be an old tns changed to a pme but if think there its been left like that cause of corrosion to there incoming cable
i remember something the DNO mentioned to me a few months back regarding an installation query i had

Please Explain what you mean??

 

[Paul.M]

Below is an install done by member Dave85. You can't get any clearer than that. Nice job Dave.

 

[Top Cat]

Below is an install done by member Dave85. You can't get any clearer than that. Nice job Dave.

Still waiting for the meter guy to to put main fuse in and seal up i see! Lol

 

[Paul.M]

Still waiting for the meter guy to to put main fuse in and seal up i see! Lol

TC let's not confuse matters lol. Besides this was an emergency job because the 3036 cu was melting.

 

[Dave 85]

To be quite honest, and I know, this is a running joke and we always say it, but this time I can, hand on my heart, say that the cut out seal had already been removed before I got there.

 

[Top Cat]

Just a quick point as this is for training purposes Paul, on the drawn TT system someone may think that water and gas do not need earthing! I know it's a stupid point but someone will..................!

Edit:- As kindly pointed out to me it should read bonding not earthing!

 

[telectrix]

TC... that TT system has all plastic water pipes and there is no gas.

 

[Paul.M]

To be quite honest gents I want other members to say things like what TC has said on this thread to expand it into a great source of information for everyone. Please continue with positive posts.

 

[Dave 85]

To be quite honest gents I want other members to say things like what TC has said on this thread to expand it into a great source of information for everyone. Please continue with positive posts.

Wow man, I must be the new Derren Brown, I just influenced your actions without you realising it. I start a post with 'to be quite honest' you 'like' it and then you start your next post with 'to be quite honest'.
Nuts to this electrics lark Im going into mind control.....

 

[topquark]

To be quite honest gents I want other members to say things like what TC has said on this thread to expand it into a great source of information for everyone. Please continue with positive posts.

Why? Are you covering DC systems as well?

 

[Knobhead]

Why? Are you covering DC systems as well?

Do you want me to start on that?

 

[Knobhead]

Just a quick point as this is for training purposes Paul, on the drawn TT system someone may think that water and gas do not need earthing! I know it's a stupid point but someone will..................!

Edit:- As kindly pointed out to me it should read bonding not earthing!

Can't be doing with fussy cats

View attachment 13130

 

[Top Cat]

Can't be doing with fussy cats

View attachment 13130

Size of earth wires?

You'l wish soon you hadn't asked for criticism!

 

[Paul.M]

Let's just keep to domestic earthing systems for now lads. I know this is basic stuff but its somewhere that the learners can Google and learn more than in a book from us lot.

It's worth the effort IMHO.

 

[Air Conditioner]

Thanks for this thread its great to see some real life pictures, rather than just the pictures in books. One thing that took me by surprise in the transition from books to real life was that the main earthing terminal is sometimes in the CU in real life, rather than a totally separate earthing bar which how it is normally illustrated.

 

[telectrix]

that used to be the norm years agoo. it's only in the last 10-20 years that a separate MET has become more widespread.

 

[Air Conditioner]

Is there a reason for this? Is it easier to measure Ze? Or the manufacturing of cheaper CU's? Or is it just the way it is?

 

[Top Cat]

What are those yellow, blue and black things!:biggrin5:

You did say you liked what TC was doing! Lol

 

[Paul.M]

Air conditioner and Tel, these are the things that I'm on about. It's great learning from books to pass an exam but its a different world out there once you pick up your tool box and go to your first job.

Has any other members got main incomers photos? Post them up.

 

[Top Cat]

Air conditioner and Tel, these are the things that I'm on about. It's great learning from books to pass an exam but its a different world out there once you pick up your tool box and go to your first job.

Has any other members got main incomers photos? Post them up.

Hi Paul, sorry if i sounded flippant with my relies but it did have a serious message. If the first two diagrams have every detail on them, the third should also.

 

[Paul.M]

Hi Paul, sorry if i sounded flippant with my relies but it did have a serious message. If the first two diagrams have every detail on them, the third should also.

No offence taken mate. If I could find the osg diagram of a TT system on Google images I would have posted that instead. Seen as I do all my posting from a mobile phone (yes, over 3,800 atm) and I've spent over an hour today on this thread to give basic learning to others. If I can put the effort in, why can't the people that are learning the trade? Let's encourage them to better their knowledge. Well I'm still learning and I'm not a half bad sparky lol.

 

[JUD]

Here's mine at home...

TN-S or TN-C-S???

Answers on a postcard :sifone:

 

[topquark]

It looks suspicously like TNCS but I'm going for TNS with that bit of GY lurking at the bottom of the head. I'm guessing you've put the REC in!

 

[Top Cat]

Here's mine at home...

TN-S or TN-C-S???

Answers on a postcard :sifone:

The seals are missing, whats the problem!

 

[Air Conditioner]

Is the telephone cord you phoning the DNO for more seals?
Its a TNCS with a TNS thrown in for good measure. Just looking for an earthing rod!!!LOL

 

[JUD]

It looks suspicously like TNCS but I'm going for TNS with that bit of GY lurking at the bottom of the head. I'm guessing you've put the REC in!

Yep TN-S. Confused Elecsa guy a bit until I told him I got higher reading on PSCC. Yep I put the REC in for convenience when changing CU.

The seals are missing, whats the problem!

Never had a seal on it.

 

[Paul.M]

I've just shown this thread to my wife and she understands about earthing arrangements! Even Juds! Tomorrow we will step it up a notch I think.

 

[steveberry11]

Is it not the case that if a TNCS system has been given this is the primary source of earthing.

Just a thought
Would the DNO then leave in the TNS connection or connect the cable sheath to the TNCS terminal if the sheath earth is suspect in the area.

One word of caution in the first photo the TNS earth connection was made via an earth strap around the lead sheath. Beware of tightening these up if they become loose as the effect is to squeeze the lead sheath into the line and neutral conductors. End result BANG.
This also used to be common on SWA cables (not sure why). The outer sheath was striped back around 100mm from the gand and a earth strap fitted around the armour. While carrying out maintenancee or periodics the straps were found to be loose so were tightened up. After several rounds of this the armours were squeezed into the conductors BANG.

Obvious I know but beware.

 

[terminator]

Paul - It may be a way to remembers the 'S' as connected to Sheath (which of course it is) - but the important point is that it actually stand for 'Separated'.
i.e. Separate Neutral and Protective conductors throughout the system.

I know that you and experienced guys know that, but I think that guys learning the ropes ought to understand the importance of that. And how it differs from TN-C-S. (PEN conductors)
T = Terra (earth)
S = Separate
C = Combined

Apologies if I've opened a can of worms. But good thread. I think that Earthing is one of the most misunderstood subjects in the trade.
Thanks anyway Paul.

 

[Paul.M]

Terminator that was tomorrows lesson/debate lol.

Terminology, especially for those taking exams are key.

Step by step, day by day this thread will grow with everyone adding to it just like you have, thank you, keep it coming.

 

[terminator]

Sorry mate, still it is nearly tomorrow! :dozey:

 

[Gravid]

Didn't fancy pulling this one.

 

[Knobhead]

Dear god! Nothing more to be said, other than where's the real service head!

 

[Paul.M]

Dear god! Nothing more to be said, other than where's the real service head!

This is what we call a TN-C-S. 'T'hat's 'N'ot 'C'onducting 'S'urely!

 

[Silly Sausage]

From a certain breed of bank...

 

[Silly Sausage]

and another one,



with associated gas bonding...

 

[Knobhead]

Spotted what’s wrong with the last picture, compression fittings on gas!

 

[Paul.M]

and another one,

View attachment 13146

with associated gas bonding...

View attachment 13147

Pic 1, don't you just love that leaky window with the slope to the electrics lol.

Pic 2, we have floating neutrals, that gas engineer has a floating pipe :rofl:

 

[StuSpiers]

PME
TNS

You decide....