TN-S Earthing Conductor

[MattH]

Quick couple of questions for the sparks:

Conclusive proof that ignorance is bliss!

After 10+ years in our house I felt the need last night to check if our supply was TN-S or TNC-S.
Turns out it's TN-S, all well and good. However, after taking some pics in the deep dark depths of the under-stair cupboard I've spotted a few concerns with the Earth bonding arrangements.

Firstly the Gas and water pipe Earth straps are bought back to the earth strip in the Consumer unit rather than an external earth block. The CU is then bonded to a 2 way earth block which in turn is bonded to a clamp on the incoming supply pipes/conduit.

From the looks of it the connection between the earth block and the clamp is being made by a bare piece of copper cable maybe 1.5mm - 2.5mm CSA!

The main 100A fuse unit looks like a TNC-S unit with provision for a PEN type Earthing terminal.

So, after all that rambling: is the Pipework bonded to the CU earthing strip OK and how should I deal with the main Earthing conductor? Can an independent Spark sort this out or does the DNO need to rectify it (if so how do I get them involved and who do I contact?).

Pic below shows the incoming pipe clamp and the tiny copper connection to the main earth terminal. The clamp is not really visible but is there under the brown/red hardened putty type stuff:

 

[Kent]

looks old, once you get a proper spark in I recon the Bill and job is going to grow and grow so be prepared. Only the energy company can work the supply side of the meter the meter its the energy supplier you use after that its a qualified spark.

 

[Wendelspanswick]

Looking at it I wouldn't be to concerned, if you want peace of mind borrow an Earth Fault Loop tester or even better get a Spark in to measure it for you.

 

[MattH]

Cheers for the replies guys.

MrFuzzy, the G/Y is the earth bond to the CU. Looks like the house had a new CU sometime prior to 2001 when we moved in. It is a modern type unit with MCB's and a double pole isolator (rather then an RCD).
House was built in the sixties and is an ex-local authority house, I suspect the rewire / CU was done by the local council when Central heating was retrofitted to all the houses in the area. Possibly back in the 80's.

The rest of the house wiring I don't really have an issue with. It was just that small conductor that had me worried when the current regs talk about 16mm2.

 

[Sidewinder]

MattH,

I can't see from your photo, but, if that G/Y is going from the earth bar in the CU to the head, and it is there connected to the suppliers earth,then it is not an earth bond, it is your earthing conductor for the installation.
I can't see any clamp in the picture.
Now if on the lower RHS that is a brass block coming out from within the head, then you have TN-C-S, not TN-S.
From your pic I cannot see a connection to any of the DNO cables which would give you TN-S.
I can't see any thin bare copper wire in your picture?

Do you have a separate building earth marshalling terminal, or is your CU earth terminal acting as the BEMT?
I'm not quite following the way you are describing things.

BTW, whilst it is the presentation of the supply to the consumer that defines whether it is TN-C-S or TN-S, in reality there is a god chance that the DNO network will be heading towards most of it being a CNE conductor anyway.

A few more pics?

 

[MattH]

Ok, so the G/Y cable loops back up to the CU, at the bottom of the earth block is a bare cable that runs to a clamp which is covered by some type of hard putty.

 

[MattH]

I have no intention of touching it.
If it is as it should be from when the DNO installed it then fine.

 

[rtbcomp]

Do they still bond to gas pipes?

I'm sure we've all heard the tale (urban myth?) of a faulty earth on a gas pipe caused a fire which melted the water pipe and put the fire out. The escaping gas was then ignited by a spark from the wet fuse box and blew the house up.

 

[rtbcomp]

^^ Pretty much what I thought. In my street they replaced the lead/iron water mains with plastic, would that compromise the earthing?

 

[brightspark]

its not earthing its bonding.if the household pipework is in copper back to the stop tap its bonded in 10,0mm earthwire close to the stop tap and back to the main consumer unit earth block . if its all in plastic inside house nothing to bond . just gas or oil depending what u have

 

[rtbcomp]

^^ Gotcha - I was led to believe it was earthing.

 

[brightspark]

depends if the waterpipe is extraneously conductive or not, even if its copper, if its not an extraneously conductive part, it shouldn't be bonded...

quite a lot of water pipes are buried in concrete floors cold water and central heating pipes and screeds so consider that as extraneous conductive parts. page 40 paragraph 4.4 in the IET on site guide

 

[Sidewinder]

OK from the further pics it is TN-S.
Now the block to the right of the head is the earthing terminal for the installation.
The connection from that to the cable is the DNO responsibility.
The wire from the block to the CU earth bar is the earthing conductor for the installation.
Now, what is the earthing and bonding arrangement from the CU earth terminal to the remainder of the install?

 

[brightspark]

some people just need to go on and on. im working in a large house at the moment. some of the pipes are in the walls some are surface and some in concrete floor . the walls are damp. an eight meter length of 10mm earthwire bonded to the water mains overcomes any doubt where the pipes are buried. tested or not

 

[brightspark]

read the book

 

[MattH]

Cheers for all the replies guys.
Sidewinder, my concerns where really around the DNO's cable to the earth terminal. Yours and others comments have confirmed that this is proper for the age of the house.
All Earth bonding is taken back to the earth strip in the CU and appears to be correct.