question on TN-S earthing

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Our system is on TN-S earthing and the connection with the supplier's cable from our earthing block is via what looks like a very small green wire not bigger than 2 or 3mm.

I've seen a sketch on the iet forum and this shows a 16mm cable.

Can we request that the DNO upgrade this or can they leave it as it is?

All the Z values tested ok as told by a spark.
 
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When you say 2-3mm, is that the outside diameter, or the CSA (cross sectional area) - the 16mm figure will be the CSA, the actual cable will be nothing like that big, although it is slightly bigger than 2-3mm.

My house has ~6 or 10mm CSA earth serving it (and the house next door which for some starnge reason runs through my earth block), which is slightly undersized, but not disasterously so (my Ze value checks out fine etc). I would suggest if a spark has tested Ze and it's fine, then you don't need to worry too much (but I'm not an electrician, so don't necessarily trust what I say!)
 
The size of main earth bond depends on your main tail size and fuse. The sparky who tested Ze for you will tell you if it's indersized.
 
If you are getting an acceptable Ze from it, then the DNO are unlikely to be interested in upgrading, unless it is single strand wire or a dodgy connection (EC14 earth strap for example).
 
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can you post a photo?

where is this thin wire connected to?
 
it is the connection between the dno cable sheath and the earth block.
the earthwire from earth block to cu is a massive 16mm.

I remember seeing a pic similar to my setup on here, i'll search for it and get back to you if i can find it
 
although it's not G&Y, it doesn't look terribly small. Are we meant to deduce that yours is the same size?

How about you take a photo of your own one, showing what YOURS is attached to at the DNO end.

//www.diynot.com/forums/viewtopic.php?t=129539

What I have in mind is that you might be able to attach a 16mm G&Y. Or maybe yours is just knotted round the sheath, or something.

I can't tell just by looking at a photo of someone else's installation :rolleyes:
 
ok i'll get a pic tomorrow.

This photo i posted seems to have two earthing connections (the green small wire and the white one) whilst mine only has the small green wire going into the cable sheath.
 
If it is the earth cable between the sheath of the supply cable and the earth block then that is the DNO's (district network operator) responsibility, and it is very unlikely that they will come out to replace it with something larger.
TBH I see loads of service heads with this type of earthing (or even thinner) and so long as the Ze is within limits I'd just put a block on it and then make sure that my side is up to scratch.

Please remember that he DNO's use a completley different set of rules and regulations to us.
 
My house has ~6 or 10mm CSA earth serving it (and the house next door which for some starnge reason runs through my earth block)

supplyearth3wqt9.jpg


:?: :?:



If it is the earth cable between the sheath of the supply cable and the earth block then that is the DNO's (district network operator) responsibility, and it is very unlikely that they will come out to replace it with something larger.
TBH I see loads of service heads with this type of earthing (or even thinner) and so long as the Ze is within limits I'd just put a block on it and then make sure that my side is up to scratch.

Please remember that he DNO's use a completley different set of rules and regulations to us.
So the point of insisting that the customer's main earth conductor is an order of magnitude larger than the one it connects to is what, exactly?
 
BAS: Yep that's how it appears (I haven't been in my neighbours house to see that end, but I have a cable coming up from the floor into the service head with an earth coming off it into my earth block, and a cable diving into the party wall betwen the two houses leaving my service head, with another earth on it going into my earth block)...

I guess there's nothing strictly speaking wrong about it, as long as I like my neighbour ;)
 
Wrong might be the incorrect word to use, it probably is wrong (it seems crazy that I can cut my neighbours earth off), but not immediately dangerous anyway at least...
 
I guess there's nothing strictly speaking wrong about it, as long as I like my neighbour ;)
It's your neighbour who has to worry - he'll have no idea, as what he will see at his end will look like a perfectly normal TN-S supply, and he won't know that his earth path is at your mercy.

If ever you see him having electrical work done, ask him to have the electrician measure his Ze before, and after, you disconnect the cables running between the sheaths and your MET (obviously with all relevant temporary safety precautions). Maybe a complaint from him to the DNO protesting about how his safety depends on something in your house might get some action from them.
 
That sounds like a good idea. I have an earth loop tester so I could offer to measure Ze for them, but it's an elderly couple who I've only really said hello to, and I don't want to upset / confuse them by just appearing and trying to explain some quite complicated things to them. I might keep an eye out for any vans and try and talk to the spark directly (I have noticed an electrician's van outside a couple of times recently, but not sure if it's for them or someone else on the terrace...)
 

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