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?

 

[Engineer54]

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.

Any thoughts on this?

Just looked back over this thread and should have mentioned that if a rod has an exothermic or brazed welded connection, it doesn't really need or warrant an earth pit enclosure, (but the rod to cable connection should still be protected, say with amalgamating tape) unless it's only for location identification purposes. I would imagine, that in this case it's one of more than one earth rod position, the first having a removable bolted clamp connection for testing purposes.

I'll assume that this rod is a part of an industrial or commercial earthing installation or maybe even a lightning protection system, rather from a domestic installation??

 

[GLENNSPARK]

Just looked back over this thread and should have mentioned that if a rod has an exothermic or brazed welded connection, it doesn't really need or warrant an earth pit enclosure, (but the rod to cable connection should still be protected, say with amalgamating tape) unless it's only for location identification purposes. I would imagine, that in this case it's one of more than one earth rod position, the first having a removable bolted clamp connection for testing purposes.

I'll assume that this rod is a part of an industrial or commercial earthing installation or maybe even a lightning protection system, rather from a domestic installation??

like a nest....

 

[Hohmage]

Hi folks. New member but regular visitor. Thank you for this very interesting thread, in a nice style too. I'm hoping to resurrect it. What do you think of this one then? I'll have more pics to follow, but what does this say to you please?

 

[Hohmage]

Another couple...

 

[Engineer54]

So what do YOU think about them??

 

[Hohmage]

So what do YOU think about them??

Hi Engineer54. The first few posts were along the lines of a quiz, so I was trying to get people guessing. Perhaps it's so obvious it isn't worth asking, in which case I'll go now! I'm no electrician, but have been told what the system is by the DNO. It's fairly unusual and outdated as far as I know, and I thought people might be interested (as the thread suggested). I have more pics, I was waiting to see if folk needed more. I was ultimately going to ask this question which I don't know the answer to: how safe is it and what can I do to make it safer!

 

[Silly Sausage]

As no one is playing Hohmage's game, I'll take a punt...

It's PNB.

Away you go fellas!

 

[aesmith]

What's going on there? It looks like two cables leaving the pole, but three arriving at the house.

 

[telectrix]

i'd like to see it with the red insulation tape removed.

 

[Knobhead]

What's going on there? It looks like two cables leaving the pole, but three arriving at the house.

There will an intermediate pole or poles with an earth rod.

 

[Hohmage]

Hi folks. yes, intermediate pole with earthing. Didn't mean to mislead anyone. The red tape isn't masking anything, it was covering the exposed copper at the meter tails. I'm guessing that the greenish wire to right of main fuse is the earth. I am trying to post more pics, but have just upgraded machine to Windows 8 and am lost!

 

[Silly Sausage]

Come on Hohmage, what did the DNO say?
Exact wording please!

 

[Hohmage]

Come on Hohmage, what did the DNO say?
Exact wording please!

Chap said "CEW". Couldn't get much more from him. I've Googled CEW and found one reference to it on this forum, someone asking a question about it but no one answered. Anyone know?

 

[Hohmage]

Is it a posh TT? Earthing cable comes down a big pole?

 

[Silly Sausage]

I've found CEW = Continuous Earthwire. (PME or PNB)

Ask on the IET Wiring Regs Forums, they're bound to know!