bathroom earthing

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bathroom earthing

Postby S Payne » Fri Oct 06, 2006 11:10 pm

i understand about the bonding of pipes radiator etc in a bathroom but am not clear if there should be a earth wire directly back to the earth at the main earth point at the meter board the installation already has an earth to the water pipe at the stopcock where it comes into the house or is this just for new installations and if it is req is it 6mm or 10 mm
as information i have found to date does not seem to clarify this properly
S Payne
 
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Re: bathroom earthing

Postby carpfinder » Tue Oct 10, 2006 8:51 pm

On your main earth you should have a earth strap on the house side of the main water tap with a 10 ml earth wire to your fuse box.
From the Fusebox there should also be a 10ml earth, to the supply head company earth. the bathroom should have earth straps round pipes at the bath, the leg of the bath if it is metal,the pipes at the sink, and at the radiator.They should have a continuous 6ml earth there is no need to go back to the fuse board, unless you have compression joint somewhere in the main water pipe, there must be mains water in bathroom continuous to main. if tank water you must go back to fuseboard
carpfinder
 
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Re: bathroom earthing

Postby Paul Barker » Mon Oct 16, 2006 9:50 am

Only a plumber, but my take:

The diameter is according to a chart in the big brown book but in most cases in the uk this is 4mm. As it has also to be taken to the protective conductors of any 230v appliances in any of the zones it gets back to the MET in that way. If there are no appliances then cage (Faraday Cage) it into a nearby protective conductor say from a light fitting or socket on ring main in adjacent room.

The principle of all this is that you are creating an equipotential zone, such that all metal parts but most particularly those which may be able to make contact with earth from outside the zone, are at the same potential. If there were a fault in this zone and every metal part stood at 230v you would not get a shock touching any two of them. If for example a water pipe came into the zone and was not equipotentially bonded to the other metalwork in the zone and then there was a fault, were you to touch the metalwork of the zone which is at fault potential AND the pipework introducing ground potential then the full current available would pass through your wet body to earth, which could be fatal.

Small pipes and metal parts that do not introduce a contact with ground from outside the zone do not require bonding. So soap trays copper pipes for heating that go to plastic pipe straight away under the floor, radiators and towel rails (even when fed from copper are deemed to be equipotential via the bonded pipework. It is also possible that a copper piped bath where the copper pipe is bonded doesn't require bonding, but best to drill a leg and bond it anyway. A plastic piped bath that isn't in contact with any metal framework in the building should not either need bonding any more than a soap dish would.

The pipework bonding can take place in an adjacent airing cupboard.

I am happy to be corrected by proper electricians as this is how we all learn.
Paul Barker
 
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Re: bathroom earthing

Postby Paul Barker » Tue Oct 17, 2006 7:42 am

The whole issue of earth bonding is steeped in malpractice. I am just a plumber but I am gaining full scope electrical qualifications, already have a level 2 part P qualification and bs2391 just need bs2381.

Every sparks I encounter on site I ask pertinent questions and they all puff out their chests face you head on, point at you and dictate how it is. The trouble is they all conflict with one another and with what I read.

Much of the malpractice stems from sparks who combine their 15th edition knowledge wherein kitchens had to be bonded, with 16th edition klnowledge, and a little extra missinformation which has lead to you in this post thinking 6mm or 10mm is required in a bathroom.

The area of central heating bonding is such a cause of local confusion I had to deep searching questions, and again there are a plethora of replies.

In short, as far as I can make out, it is being overdone and oversized.

What we have to do is come back to the basic understanding of what we are doing when we bond, and of the locations where we are required to provide an equipotential zone. Those areas are not boiler rooms or kitchens.
Paul Barker
 
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Re: bathroom earthing

Postby S Payne » Tue Oct 17, 2006 8:58 am

hi all
thanks for replying to my questions and your right i too have had different responses from different electricians as well it seems some say 4 mill minimum so you can fit 6 if you want and you use one continuous length for the bonding from taps to the light fitting
Nowhere does it tell you how you get that large wire into the earth on the light though
i have found on the nice site a pdf nl139supp.pdf
which gives pics and explanations
http://www.niceic.org.uk/downloads/nl139supp.pdf
but this has a date of 2001 but i think it does help
with the pics well i think they should know if anyone does anyone know anything more?
especially how to connect to the light fitting?
S Payne
 
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Joined: Tue Oct 17, 2006 12:59 pm

Re: bathroom earthing

Postby Paul Barker » Tue Oct 17, 2006 7:51 pm

This is why you should use 4mm.

What you have to do is create your own earth block next to the light fitting, take a wire that you can get in from the light fitting to your terminal and terminate your 4mm there.
Paul Barker
 
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