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Earthing Arrangements Explained + Photo's

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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.


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.


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.


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?

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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.
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)


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!
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?

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!!)

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!!
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