Supply Earthing

[Vic Water]

Thanks guys

"split concentric - TN-S", don't know what that means but maybe the grey box was also already there and they just put the new cable into it - I can't remember.

What is Ze and how is it measured?

Do I actually need an electrician to come in and do something? If so, it's a bit much for the water board to do something that means I have to pay the electricity 'someone' to do something else when it was all fine before (except for the huge amount of wasted water from leaky pipes I suppose).

Just a thought. They are lining (or replacing) the old pipes with plastic ones. I imagine that this will only go from the mains up to the point of entry at my house (stopcock is in front of property in garden - not in the house). From there it is a lead pipe until it gets into the house and then copper once in the open again. So is underground from front gate - about 15 feet I guess. Does that also provide some/enough earthing?

 

[Lectrician]

The water pipe does not supply you with an earth - in the old days it did. Your earth is supplied by the supply cable, although you must still "earth" your water pipe within 600mm of entry to the building - this is for "safety shock protection".

The service head used is a PME head, with no provision for splitting the neutral and earth block within. They have used a split-con cable which provides a split neutral and earth. As the head doesn't have provision for an earth, they have taken the bare earth out of the head, and bodged an earth terminal.

I can 99.99999% guarantee that it is split-con cable, and the bare copper you see is the 4 earth strands. I would deffinantly say that the earth is continuous through the service head, but couldn't guarantee if it earthed at the other end under the road!?!

 

[ban-all-sheds]

Thanks guys

"split concentric - TN-S", don't know what that means but maybe the grey box was also already there and they just put the new cable into it - I can't remember.

What is Ze and how is it measured?

Split concentric

TN-S

Ze is not so quickly explained - if you look at the diagram of the components of an earth fault loop here, Ze is the external part - the sum of items 7, 8, 9, 10 & 11.

The rest of Chapter 5.3 will explain why it's important, (as will this, but you need to scroll down to "Post Subject: TYPE B, C MCBs - What's all that then?", as the positioning is screwed....)

This talks about measuring Ze.

 

[Steve]

Just a thought. They are lining (or replacing) the old pipes with plastic ones. I imagine that this will only go from the mains up to the point of entry at my house (stopcock is in front of property in garden - not in the house). From there it is a lead pipe until it gets into the house and then copper once in the open again. So is underground from front gate - about 15 feet I guess. Does that also provide some/enough earthing?

our incoming water main is lead too. They "relined" the water mains a couple of years ago, but didn't touch the feeds to houses. You really ought to have a stop cock at the point of entry to your house too. And earth continuity to the water mains does not matter in the slightest.

 

[Vic Water]

Thanks again for the feedback.

Lectrician – why wouldn’t they connect the earth under the road if they had to wire the cable in anyway?

The only reason I asked about whether the length of lead pipe would provide sufficient earth is that THAT is connected to my electricity consumer unit via the earthing stud. How much metal has to be under the ground to provide sufficient earth? Obviously I want my electricity supply to be as safe as possible with adequate earthing.

Ban-all-sheds – thanks for the info. I understand the Split concentric and TN-S references now. As for Ze that seems a little beyond me I’m afraid.

Crafty1289 – Nowhere to put a stopcock in my house without ripping apart something. The stopcock by the front gate is easily accessible if not convenient. Did you have to have a new earth fitted when they relined your pipes?

All – I have RCD in my split consumer unit. Will this still trip or indicate a problem if the earthing is compromised due to the watermain relining?

 

[Steve]

ok, some misunderstanding i think. The earth wire attached to the main pipe is NOT meant to the be main earth for your system. Years ago, it was. Now, it is for MAIN BONDING which aims to ensure that every extraeneous metal conductive part is bonded to earth, to reduce the risk of electric shocks from the extraeneous parts introducing voltages into the equipotential zone. There will be one to the gas main too. DO NOT WORRY about the length of copper or lead underground, it is of no consequence to your safety. Your installation appears to be adequately earthed via the split concentric cable coming into the house. If you are still concerned, ask an electrician to conduct an earth loop test.