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?

 

[Hohmage]

The advantage of having sheep and cattle in the field is you know there’s a ground voltage gradient around the switch. Dead sheep and cows tend to give it away.

Okay, thank you Tony. I usually do my best to keep the sheep out, but will now go and tear holes in the fence.

 

[GLENNSPARK]

The advantage of having sheep and cattle in the field is you know there’s a ground voltage gradient around the switch. Dead sheep and cows tend to give it away.

yes Tony...

 

[zap]

Can anyone identify which type of supply this is please?
It looks like 16mm2 twin and bare earth.

 

[topquark]

Nope, not from that pic, but I'd hazard a guess that's a submain with EMT, the question is where from.

 

[zap]

I think it's a 60's build council semi near Poole, Dorset. It's no longer council though.
I'm not sure how to proceed. I suppose a call to the dno should be the next step.

 

[topquark]

Where is the service fuse? Is this flats (possibly three phase with a phase/flat etc). That doesn't look like the main head to me.

 

[zap]

It's a semi-detached house with a pre-paid meter and cut out within the same enclosure (I think!).
The property is some distance from me so I'll ask the client (a friend) for another picture showing the content of the enclosure and when I get it I'll post it here.

 

[zap]

Deleted... only I haven't worked out how to delete the photos! Help!!

 

[zap]

Where is the service fuse? Is this flats (possibly three phase with a phase/flat etc). That doesn't look like the main head to me.

Sorry for the delay, 415V ???

View attachment 22379View attachment 22380View attachment 22381

 

[Engineer54]

The incoming cable looks like a split concentric and so will be TN-S. I assume that the G/Y earth cable is the main earth to the remote CU. If in doubt test for TNC-S!!

 

[zap]

The incoming cable looks like a split concentric and so will be TN-S. I assume that the G/Y earth cable is the main earth to the remote CU. If in doubt test for TNC-S!!

Thanks Eng. Yep, G/Y is the main earthing conductor. I'm sure determining the pfc will reveal.

 

[DPG]

Why do you say 415V ? Daz

 

[zap]

Why do you say 415V ? Daz

the information on the cut out (pic 3) says:

series 7 415V BS1361 100A type IIb

 

[DPG]

Though it might be that. Don't assume it's 415V because it says it on the side. In a similar way, don't assume it's a 100 amp fuse because it says 100A on the fuse carrier. Daz

 

[zap]

Why do you say 415V ? Daz

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