Electrical earth ground for UK homes (not quite boaty)

[haydude]

I live in a UK fairly modern and relatively (for uk standards) well built home (about 14 yo).

I was wondering how the electrical earth/ground system is connected in UK homes.

In my country there is normally a well marked copper rod that goes as deep as the soil requires. The rod normally has an access pit for maintenance which is used to pour down water and salt during particularly dry spells.

However I do not see anything like it around any UK home. Someone told me that in the UK earth is connected to water pipes, but modern water mains are blue plastic hoses which practically isolates any such earthing making it useless.

I was wondering if someone with some knowledge could enlight me.

 

[prv]

Homes in town fed by an underground supply cable generally take their earth from that cable. There are two ways of doing it, but I can't remember the subtle differences between them. The supply cable is connected to earth at the local substation.

More rural places, further from the substation and often fed by overhead cables, do have an earth rod as you describe.

Pete

 

[VicS]

There are several ways in which the earth may be provided.

there is a fairly good explanation of the different systems in Wikipedia:-
http://en.wikipedia.org/wiki/Earthing_system

Trust your electricity supplier to have correctly provided the appropriate earth connection.

Because water pipes tend to be plastic many things in the home that might have naturally been earthed via a metal water pipe must be earthed to the earth in the electricity supply. Internal copper plumbing and metal sink units come to mind.

 

[kindlebooks]

I ran a large earth cable from my consumer unit through the wall to a 3 foot copper rod hammered into the garden (away from humans). Right or wrong, I don't know. Couldn't hurt as a backup could it?

 

[TrueBlue]

In this part of the world, folks who live in towns have their 'leccy supplied via armoured cables which is eather.

Out here in the countryside,

where the cows do poo,
and the birds do sing,
hey ding a ling

our supply comes from overhead cables and in some areas the neutral wire is earthed by the supplier putting a long copper rod in the ground. but not always. SO houses are required to have not one rod but several laid out in a grid instead and ignore the PME bonding because this causes other problems...

 

[AntarcticPilot]

There are several ways in which the earth may be provided.

there is a fairly good explanation of the different systems in Wikipedia:-
http://en.wikipedia.org/wiki/Earthing_system

Trust your electricity supplier to have correctly provided the appropriate earth connection.

Because water pipes tend to be plastic many things in the home that might have naturally been earthed via a metal water pipe must be earthed to the earth in the electricity supply. Internal copper plumbing and metal sink units come to mind.

Indeed. All internal metal pipework is required to be earth bonded under UK building regulations, and if an electrician or plumber works on your house and finds it isn't (say, an old, pre-regulations house), he/she will insist on doing it - and won't allow your house to be reconnected to the supply until it is.

It is obvious if it has been done - there will be yellow and green coated wires all over the place!

 

[prv]

Indeed. All internal metal pipework is required to be earth bonded under UK building regulations,

Only if they're "extraneous conductive parts" though (I think that's the magic phrase). My house water supply is a plastic pipe, so although it immediately switches to copper after the internal stop-cock, the pipes don't appear to need bonding (they aren't, anyway) because they're not connected to an earth outside the house. Metal structural elements have to be bonded too, assuming they run into the ground. I don't have any structural metal in my house, but my tin shed is bonded to the supply earth (which is a rod, because it's too far from the house to safely export the earth from there).

A few years ago I understood all this stuff

Pete

 

[AntarcticPilot]

Only if they're "extraneous conductive parts" though (I think that's the magic phrase). My house water supply is a plastic pipe, so although it immediately switches to copper after the internal stop-cock, the pipes don't appear to need bonding (they aren't, anyway) because they're not connected to an earth outside the house. Metal structural elements have to be bonded too, assuming they run into the ground. I don't have any structural metal in my house, but my tin shed is bonded to the supply earth (which is a rod, because it's too far from the house to safely export the earth from there).

A few years ago I understood all this stuff

Pete

Um. I am not a plumber, merely a house-holder who has had work done fairly recently, and have just bought a new-build house. Our plumbing is all earth-bonded, and whatever they used for mains pipes in 2011 is what we have! FWIW, I think the mains pipe is a blue plastic pipe.

I'd actually have thought that it was wrong way round the way you say - that if it ISN'T connected to a good earth, then it should be earth-bonded, so you can't get the plumbing at mains voltage in the event of a short circuit.

However, I am NOT a plumber, and stand to be corrected.

 

[prv]

stand to be corrected.

I stand to be corrected too. Too many years since I needed to worry about mains electrics.

The uk.d-i-y newsgroup contains many knowledgeable people; this page is from their FAQ wiki and seems like a reasonable summary. It seems some of what I said was wrong

Pete

 

[RichardS]

Um. I am not a plumber, merely a house-holder who has had work done fairly recently, and have just bought a new-build house. Our plumbing is all earth-bonded, and whatever they used for mains pipes in 2011 is what we have! FWIW, I think the mains pipe is a blue plastic pipe.

I'd actually have thought that it was wrong way round the way you say - that if it ISN'T connected to a good earth, then it should be earth-bonded, so you can't get the plumbing at mains voltage in the event of a short circuit.

However, I am NOT a plumber, and stand to be corrected.

I think you're right.

Our house was built in 1998 and the incoming water pipe is plastic and only changes to copper after the main stopcock so every single pipe run and every radiator has ugly clamps and very thick green and yellow cable connected to them.

I reckon that this is the usual "health and safety gone-mad" as, at some point, all the heating metalwork is connected to all the other heating metalwork and all the clean supply is connected to all the other clean supply so, in extremis, you only need one earth point on each.

Every time I do any plumbing or re-wiring I get rid of all this carp!

Richard

 

[maxi77]

There are several ways in which the earth may be provided.

there is a fairly good explanation of the different systems in Wikipedia:-
http://en.wikipedia.org/wiki/Earthing_system

Trust your electricity supplier to have correctly provided the appropriate earth connection.

Because water pipes tend to be plastic many things in the home that might have naturally been earthed via a metal water pipe must be earthed to the earth in the electricity supply. Internal copper plumbing and metal sink units come to mind.

Trusting your supplier is not always a good thing, it took my mums supplier almost 100 years to realise her street had no earth connection, mind you all that was required was a connection from the house earth to the armour on the supply cable. the house had been rewired several times in it's life and no one had noticed.

 

[starfire]

I think you're right.

Our house was built in 1998 and the incoming water pipe is plastic and only changes to copper after the main stopcock so every single pipe run and every radiator has ugly clamps and very thick green and yellow cable connected to them.

I reckon that this is the usual "health and safety gone-mad" as, at some point, all the heating metalwork is connected to all the other heating metalwork and all the clean supply is connected to all the other clean supply so, in extremis, you only need one earth point on each.

Every time I do any plumbing or re-wiring I get rid of all this carp!

Richard

That used to be a problem with some of the silly rules enforced by the YEB (Yorkshire Electricity Board) at one stage they insisted that metal window frames be earth bonded !

There are now clearer definitions & tests for what needs to be and what need not be, bonded.


In the UK there are 3 main types of earthing systems.


TNS - The Electricity company supply the earth.

TNCS or PME - The Electricity company supply the earth, but this is provided by connecting to the Neutral at your supply point, there are strict rules as to the size of any earthing conductors, and any external supplies (to the shed, swimming pool etc)) cannot use this earth, you MUST use TT, see below.

The Electricity Board undertake to earth the Neutral at several points on the supply cable, normally wherever there is a service joint.

TT - No earth provided, you supply your own via an earth rod or mat, you MUST use an RCD on the incoming supply.


The idea behind supplementary earth bonding of pipework & metalwork is that under fault conditions, where there may be several hundred amps flowing through the earth connection, your bit of the earth connection may rise up to supply voltage above true earth (a screwdriver stuck in your garden) for a brief period, until the fuse blows/mcb trips.

The supplementary bonding ensures that everything you can touch or come into contact with, is at the same potential, so while you may be touching a sink that is at a 100 volts or so above true earth during a fault, Everything else is at the same voltage, therefore, no shock risk.

Apologies for the simplification of a quite complicated area.


More on topic, while the buildings in marina may use an PME earth, supplies for use by boats MUST be isolated from that PME earth & must use TT.

 

[Jim@sea]

My house was struck by lightening. In actual fact my TV Aerial. The shock went down the cable and blew up my recorder. My recorder was not covered by insurance as its only what is actually struck by the lightening which is covered.

 

[lw395]

I think you're right.

Our house was built in 1998 and the incoming water pipe is plastic and only changes to copper after the main stopcock so every single pipe run and every radiator has ugly clamps and very thick green and yellow cable connected to them.

I reckon that this is the usual "health and safety gone-mad" as, at some point, all the heating metalwork is connected to all the other heating metalwork and all the clean supply is connected to all the other clean supply so, in extremis, you only need one earth point on each.

Every time I do any plumbing or re-wiring I get rid of all this carp!

Richard

I take a more balanced view about earth bonding.
I once had the experience of drinking out of a tap that was not earthed to the same earth as the sink or the wet floor or something, it was memorably unpleasant!
Also, it is worth making sure the two sides of your CH boiler are bonded across, as small currents through the different metals are a common cause of early failure.

You can get quite significant voltages out of different 'earths' due to induced currents and other effects. Some people have even managed to extract power from the difference between mains earth and ground earth, but this is frowned upon!