Posted By Is Kismet
I have the impression (not backed up by any evidence!, or at least probably eons ago) that metal sinks should be bonded to earth. And that the contact between tap and sink is not sufficient, it has to be a separate earth link between the cold water pipe and sink.

Can anybody point me in the right direction.

Many thanks.

Is

Posted By Morgan Healey
Yes metal sinks should be bonded in addition to hot and cold supppy pipes. The same applies to cast iron and pressed steel baths.


Morgan

Posted By Edward Shyer
Hi Is,

Presume you are in the UK.

Reference:

The Institute of Electrical Engineers Wiring Regulations.
And Part P of the building regulations 2005

Regards
Ted

Posted By Jeffrey Watt
Isabelle

The answer is "it depends" on the sink, certain commercial sinks may require supplementry bonding as can be seen here,

http://www.niceic.org.uk/approved/quest4.html

For your benefit copied below.

Does BS 7671 require supplementary bonding to be applied in a kitchen?

Commercial kitchens

Commercial kitchens are not generally considered to be locations where there is an increased risk of electric shock. They are not amongst the special locations covered in Part 6 of BS 7671 and there are no specific requirements in BS 7671 to provide supplementary bonding within a commercial kitchen environment. Main bonding, however, is required to any metalwork which is an extraneous-conductive-part in its own right. For example, where a metal sink or other metallic kitchen unit, has metallic supports fixed into an uninsulated ground floor slab, making it 'earthy', or fixed steel racking is an extraneous-conductive-part in its own right, it must be main bonded in accordance with the requirements of Regulation 413-02-02.

Metal tables which do not form part of electrical equipment are not required to be earthed (or bonded unless they are extraneous-conductive-parts in their own right). Where portable equipment is used on or close to metal tables additional measures may be necessary to reduce the risk of damage to flexible cables or cords. For example, flexible cables or cords may need to be supported from above to prevent accidental damage, or additional mechanical protection may need to be considered.

Where there is a risk of damage to flexible leads supplying portable equipment on metal tables, circuit protection using an RCD should be considered. An RCD having a rated residual operating current of 30 mA or less will provide supplementary protection against direct contact.

Domestic kitchens

Domestic kitchens, cloakrooms, bedrooms and toilet areas which may contain a sink or hand basin but do not contain a bath tub or shower are not among the special locations covered in Part 6 of BS 7671. There is usually no reason why such rooms should be considered as locations of increased electric shock risk requiring the provision of supplementary bonding.

History
The 15th Edition of the IEE Wiring Regulations required supplementary bonding to be applied to all sinks where extraneous-conductive-parts were not reliably connected to the main bonding, and many examples still exist today. This requirement was deleted in subsequent editions of the Wiring Regulations and it is not required by the present Standard, BS 7671.


Jeff

Posted By Is Kismet
Thanks for your help guys, it saved me a lot of hassle.

Ismael

PS: Happy to help you Ted in the future, but today was a hassle day so I don't need your comments.

Posted By Exdeeps
Hi,
From an electrical point of view, you need to ask yourself "what can I touch that is live at the same time as I touch the sink"? If you then provide a path to earth via the bonding you then introduce a shock hazard. If on the other hand there is no or a very poor path to earth the shock hazard is eliminated or reduced. Bare in mind that most modern plumbing relies on plastic fittings and you can conclude that the metal sink is in fact a "floating neutral" and will assume the potential of whatever it is in contact with it(You holding on to a live conductor). As there is no path to earth no current will flow and therefor no shock. If you bond the sink to earth you will get a belt. Finally, if you bond the sink you could potentially transmit a fault condition to the sink causing it to become live at some future date, for example if the installation is incorectly fitted or modified incorectly.
I hope this makes sense but it's late and I am tired.
Jim