Bathroom electrics
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Joined: Tue Dec 23, 2008 11:43 am

Bathroom electrics

Post by DCMartin » Tue Dec 23, 2008 12:11 pm

Am about to completely refurbish the bathroom and install a new extractor fan, wall fan heater and 2 ceiling lights. All these are suitably ISP rated for their locations. Presumably, as the two fan devices will be run off the ring main which is protected by an RCD in the consumer unit, they will not need to be protected by extra RCD's.
However, the present lighting wiring consists of only separate L & N single cables. Can I run a separate earth cable to the area & connect all 3 cables to an independent RCD mounted near the top of the bathroom wall (zone 3), and then run new twin & earth cable from the RCD to the lighting pull-cord ceiling switch, and then on to the ceiling lights. If so, what rating single earth cable should I use? Must get this right for inspection as I do not want to have to alter things once I have retiled the bathroom!


Post by ericmark » Tue Dec 23, 2008 8:45 pm

543.6.1 Where overcurrent protective devices are used for fault protection, the protective conductor shall be incorporated in the same wiring system as the live conductors or in their immediate proximity.
This means it is just as easy to replace lighting cables as to run in just an earth. Remembering if the earth is not combined with the line and neutral it needs to be at least 4mm.
The idea of using a sub-mains distribution unit or mini consumer unit maybe is the way forward but if in England or Wales you will need Part P. Scotland have their own regulations which it seems are more stringent.
If you are going through the local authority you will need to get them to agree with your proposals and if through a registered electrician then he will need to agree.
To advise without seeing the job can really cause problems so I think you need to ask who ever is going to sign off the job.
You also talk about Zone 3 and there is no Zone 3 in a bathroom anymore.
Are you aware the old 16th Edition wiring regulations has been replaced with 17th Edition and some requirements have been dropped and some have been added.
This includes cables buried less than 50mm in a wall now need RCD protection and all electrics within a bathroom need RCD protection.


Post by ericmark » Wed Dec 24, 2008 9:32 am

Zone 0 basically inside the bath, zone 1 goes up to 2.25meters, zone 2 goes out horizontal 0.60 m from zone 1 there is another horizontal limit of 3 meters from zone 1 before socket outlets can be fitted which is really for when one fits a shower in a bedroom.
Anything in Zone 1 and 2 needs to be IPX4 and regulation 701.411.3.3 needs RCD protection for all circuits.
Where the location containing a bath or shower is in a building with a protective equipotential bonding system in accordance with Regulation 411.3.1.2, supplementary equipotential bonding may be omitted where all of the following conditions are met:
(i) All final circuits of the location comply with the requirements for automatic disconnection according to Regulation 411.3.2
(ii) All final circuits of the location have additional protection by means of an RCD in accordance with Regulation 701.411.3.3
(iii) All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2.
NOTE: The effectiveness of the connection of extraneous-conductive-parts in the location to the main earthing terminal may be assessed, where necessary by the application of Regulation 415.2.2.
Also if you read Best Practice Guide 1 at ... uides.html this may help on earth question for lights.
Inspections are normally carried out in stages called normally first and second fix. You should have an inspection before you tile. The Part P when done by the council seems to be a little open as on one hand it is suppose to follow BS7671 which means the person responsible for site safety i.e. LABC should inspect as the job progresses and issue an installation certificate but it also states under Part P the LABC will not issue an installation certificate only a completion certificate.
As electricians the problem does not arrive as we write out the installation certificate it is only an issue with the DIY man as a result don’t really know how this problem should be addressed.
It is normal to run fans from lighting to make the switching on and off with lights easy but as an alternative duel pole lighting switches can be used so electrical separate but switched together. Some fans require a max of 3 amp fusing and the alternative method is only real way to fuse down to 3 amp rather than normal 6 amp used with lighting.
I am lead to understand one should submit all this to council when applying for Part P but a recent discussion on a professional forum seems to say the councils are not following the legal requirements and in many areas Part P as run by the councils has become a farce. Including councils charging extra fees for inspections for which they should foot the bill. But of course since this is only a problem with DIY people who in the main don’t know what the council should be doing for their money the councils are getting away with it.
There is a link to Part P in projects area if you haven’t already down loaded a copy I would do. It may save you some money. It has not been up-dated since June so for forms go to ... /index.cfm you can download BS 7671:2008 forms which are up-dated and haven’t got “On line edition” printed all over them.
Normally I would have waited for your reply but since Christmas not sure when posts will be cleared so thought I should give a little more info without waiting for request.
Merry Christmas Eric

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