Earthing systems

[ezekiel]

what is the easiest wasy to tell what type of system you have TT is simple to tell but even after reading wikki cant tell between tnc or tncs any help appreciated as usual

 

[sijaysee]

tns will be a sheathed incoming main cable and will usually
have an earth off of the sheath which is soldered

tncs incoming will just be phase/neutral and is usually identifiable
by a block on the cutout by which an earth is connected

 

[RF Lighting]

unless of course it is a split concentric supply, then the cutout will look the same as a PME cutout, but will infact be a TN-S.


You also occasionally find a PME supply with a connection to the sheath, where the cable sheath has perished

 

[ezekiel]

thanks bit clearer now

 

[RF Lighting]

If you use a low range ohms meter, and carry out a continuity test between neutral and earth, it will give you a reasonable indication of the supply type.

TN-C-S should read very low, something like 0.01 ohms, as they are connected together in the cutout.

TN-S will read a bit higher, as they are not connected together in the cutout. They maybe jointed as near as in the street outside the property, or maybe not right until the LV transformer.

 

[Lectrician]

Doing as RS says, the readings may jump all over the place, expecially on a TN-S due to network current in the conductors that you are trying to push 9vDC down!

 

[ezekiel]

Thanks for all the info still cannot quite tell for sure, heres a pic
http://img523.imageshack.us/img523/7152/p1010667xz5.jpg

Can any of you guys tell by looking?

 

[Spark123]

Please can you post a bigger pic?

 

[ban-all-sheds]

TBH I can't see any main earth conductor at all on that picture - any chance of a bigger one?

[EDIT]
Doh!
[/EDIT]

 

[ezekiel]

http://img47.imageshack.us/img47/893/p1010667ia8.jpg

 

[Spark123]

I still can't see any earth wires going to the service head!!
From what I remember of the original pic the CU had a main switch (not an RCD)?
Please can you post a close up of the CU so we can see where the big earth wires are running, can you see if any run up to the service head?

 

[ban-all-sheds]

I still can't see any earth wires going to the service head!!

I was going to say that, but this time I checked first to see if I'd been beaten to it...

I can see one G/Y in the bunch at the bottom (love the chasing job, BTW... ) - could be a main bonding cable, or it could be on its way to an earth rod.

Main incomer is clearly just a switch.

 

[Spark123]

Yeah, I didn't give the picture long enough to load

How old is the CU? What certs have you got for it?

 

[ezekiel]

its only since i started college that am starting to pay attention - i lived here two years now and (although not certain) believe the house was done up for a quick sale as it appears to of been rewired ie: new sockets and a lot of them etc also it was re-plastered and as i have been a plasterer for twenty years i can tell the standards arnt great - and i recieved no certificates on purchase - starting to worry a bit now



also would it be safe to turn of at switch and rewire the cu as its a mess im quite confident at doing it as im not altering the circuits just tidying up cables?
close up of cu

 

[Spark123]

Brown 2.5 on a 40A MCB?
The far left hand side 16mm earth cable, can you see where it goes to?

Edit: are you on an overhead supply?