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PostPosted: Fri Aug 12, 2005 3:44 pm 
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Hi,

I am currently working on a section for electrical earthing/bonding in the home.

Whilst I understand the main bonding- ie. the gas and water pipes at entry to the property must be earthed back to the consumer unit or main earthing terminal using 10mm earthing wire.


I do not however understand supplementary bonding :?

A wire of no less than 4mm should link all metal pipes in the bathroom, such as sink and bath pipes as long as they are metal. Metal baths also need bonding as does the radiator pipes and any electrical equipment in the bathroom such as shower, light etc.

From what I can find this earth wire MUST NOT LEAD DIRECTLY back to the consumer unit but should be wired to the nearest lighting point or socket!

This makes absolutely no sense at all to me :?

Can someone please explain :?:

Thanks in advance

chez

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Last edited by ultimatehandyman on Sat Aug 13, 2005 9:04 pm, edited 1 time in total.

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PostPosted: Sat Aug 13, 2005 9:03 pm 
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I have found the answer to this question eventually on the screwfix forum, Thanks to the guys that answered my post!

http://www.screwfix.com/talk/thread.jspa?messageID=210080&#210080

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PostPosted: Thu Aug 18, 2005 4:21 pm 
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Hi, I found this post on the IEE website-

John peckham seems to ba a lecturer from the IEE!

If the metal work is outside the premises it is outside the equipotential zone so does not need bonding.

Taking an equipotental bond back to the MET is not required but does no harm. The idea of equipotential bonding is all in the name ie. to ensure that all the extraneuos metal and exposed conductive parts in the zones are at the same potential. This could be any voltage from 0-230V but preferably 0. If everything is at the same potential then if 2 parts of the body touch different bits of metal then there will be no current flow and hence no shock. If you have no CPC terminals in the zones the supplementary bonding does not have to be connected to one.

Taking the supplementary bonding back to the MET does no harm as it will effectively clamp the bonding to supplied earth.
Some people say this might introduce a potential in to the bathroom which hopefully it does ie earth potential. However it does not matter if it is some other potential as everything will be at this potential.

Where you may come unstuck is in places where there is a TNCS supply on a long cable run with plastic water and gas mains. The bonding must be in place anyway but you can have a difference between the supplied earth and the general mass of earth. This will show up in club and swimming pool changing rooms with concrete floors. People in contact with the pipework and the concrete floor will experience "tingles" and mild shocks. If the incomming neutral was to be lost they may suffer a fatal shock. That is why TNCS is not permitted in swimming pools, and caravan supplies.


Regards


John Peckham


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