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?

 

[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....

 

[topquark]

Hmm another punt .... I'll go for TNS again.

 

[Silly Sausage]

TNCS...???




Tea 'n' Cups & Saucers. :crazy:

 

[Richard Burns]

Few domestic TNS. One with boxed in earth connection, one with looped supply and one with the "standard" earth clamp!

 

[Silly Sausage]

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

That's I usually think, but the handfull of domestic gas isolators I've fitted on hobs, only been able to find compression valves. Have to check my CORGI registration/training course folder on that one. You being industrial with multiple bar gas lines it's probably a complete No No.

That 'Electric Shock Treatment' poster next to the flailing bond quite amuses me.

 

[Geordie Spark]

Here's mine at home...

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

Answers on a postcard :sifone:

Is that curly wire your meter by pass??

 

[Geordie Spark]

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

Nah!! ............ compression fittings are perfectly OK in an accessible place - jut like leccy junction boxes are .......... It's the floating earth that's the problem.

(but you knew that already)

 

[Geordie Spark]

and another one,

View attachment 13146

with associated gas bonding...

View attachment 13147

In pic 1, at the top right hand corner, there's what looks to be a gas Emergency Control Valve & associated pipework which looks to be far too close to the leccy stuff.

(Aye .... aahh knaa it's got nowt to do with earthing etc. aam just showing off)

 

[Silly Sausage]

In pic 1, at the top right hand corner, there's what looks to be a gas Emergency Control Valve & associated pipework which looks to be far too close to the leccy stuff.

(Aye .... aahh knaa it's got nowt to do with earthing etc. aam just showing off)

Spotted!

It was about 3am at the time, out of hours bank inspection.
I'm sure the next guy will pick it up in about 2 years time.
Banks are in pain in the proverbial. I seem to remember it takes them about an hour or so to shut down their main server (or whatever it is) so you can test the one circuit, with some clueless staff member hanging around asking how to do it - ring your IT dept!

 

[Paul.M]

On a TT system an earth electrode (aka earth rod) needs to be installed. The rod needs to be available for inspection and testing, this can be achieved by an earth pit as below.

Or if in a cellar it can be left without an enclosure. I know the picture shows a rod outside next to what looks like a metal gas pipe, I would try and locate it away from the pipe and foundations of the house and into better soil, away from concrete and rubble but if it gives you a good Ra result (Ze for a TT) I would leave unless it causes an issue with the gas incomer. Any thoughts on this?

 

[Engineer54]

but if it gives you a good Ra result (Ze for a TT) I would leave unless it causes an issue with the gas incomer. Any thoughts on this?

1/ As you say installed far too close to buildings external wall.

2/ No thread visable so probably one of those thin twigs, ...Or a threaded rod that's been chopped because they hit rubble (see 1/ above). In both cases this rod is unlikely to be stable through lack of depth!!

3/ Exposed rod to conductor connection, absolutely no protection being offered to the actual connection that is also far too far out of the ground..

4/ Area of influence of the rod will be affected by the metallic pipe, (That's if this rod is achieving anything in the first place...lol!!)

5/ Hmmmm, ...I wonder how long that external unprotected galvanized pipe is going to last? Pretty sure that doesn't meet gas codes, ...none that i know of anyway!! lol!!