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RCD Spurring

Postby misterdun » Wed Jul 16, 2008 1:16 pm


I am currently refitting a bathroom which has an existing electric shower connected to a dedicated RCD. The shower is going but I am looking to fit undertile heating, an electrical element for a towel heater and also a new extractor fan/light. I was hoping to use the RCD for the undertile heating but can I then spur off to the other devices or do they need to be on seperate RCD's? I am hoping to do the work myself and get it tested by a local sparky, is this a good idea?
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Postby sparx » Wed Jul 16, 2008 9:52 pm

Hi, no it's a very bad idea!! No registered leckie can register work done by you with building control which must be done as all the work in a bathroom comes under building regs Part P.
First of all the current rating of the showers MCB will be too high, unless you meant it is a pumped 'power shower' not an 'electric' shower.
It may be possible to use one RCD to what you want but you would need to run to seperate Fused Connection Units for each item as fuse ratings will vary, not realy a DIY job,
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Postby misterdun » Thu Jul 17, 2008 7:13 am

Thanks for the advice Sparx. The undertile heating needs to be connected to a 30mA RCD which I'm pretty sure the existing one is. There is nothing stopping me installing the consumer units and then getting a qualified person to connect it all is there? Would it possibly mean having a new consumer unit and running new cabling from there, would that be really expensive?
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Postby ericmark » Wed Jul 23, 2008 11:21 am

Dear Misterdun,
I think you should follow links in Projects to Part P. The problem is with whom can sign what. If a registered electrician designs, installs and tests a job he can issue a installation certificate and a building control completion certificate but if he only does part of the job he can sign the part he has done on the installation certificate but can’t issue a building control completion certificate. So where part of the job is done by the house holder and part by the electrician before the work is started the LABC needs informing and fees paying and once the installation certificate is completed with all signatures it needs submitting to them and then they issue the building control completion certificate.
As to the job itself there are consumer units designed for bathrooms which can be let into a plasterboard wall rather than the normal surface versions so a single supply to a single RCD could feed multi items. But with the new 17th Edition all wires need protection and I would think the only way would be to have the RCD at the origin of the supply cable this could be an advantage allowing a standard 4 way bathroom consumer unit to contain 4 MCB’s but it would likely mean the main consumer unit would need changing to one with double RCD’s fitted.
There are of course many options including use of special cable which does not need RCD protection but even the electricians are having problems in working out what is and what isn’t allowed now and to do work then find the guy who is going to sign your inspection and test part of the installation certificate does not like what you have done is a problem best avoided. So getting an electrician to do the work on a hourly rate and assisting him to speed up work may help but laying cables then asking him to connect is very likely to cause you many problems. Remember some of the rules only came in at beginning of this month so old installations although OK as they are if modified by adding circuits may no longer comply so very hard to give any advice without seeing whole installation.

Yours Eric

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