oval conduit and dot'n'dab


Postby ozmondo » Wed Jun 04, 2008 7:51 pm

Hi there.
I'm about to start wiring a house we're building. I'm not an electrician but am ok with most things. I've got someone lined up to inspect and test everything i do aswell so we should be safe!

Here's my question: someone just told me I can run cables in oval conduit on my walls and still dot'n'dab over them - no chasing required. Is this true? I can't help thinking there'll be bulges above all my sockets!!
This would save a truck load of chasing work.
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Postby ericmark » Thu Jun 05, 2008 3:55 pm

House wiring has to be registered with building controls. There are two ways to do this, either direct or by using a clearing house and becoming registered. The latter needs the registered person to sign all parts of the certificate which they are only allowed to do if they complete the work in total that’s design, installation and inspection and testing. If the work is split then the registration can’t be used and it all has to go direct through building control and even if you want to on a new house no real way to avoid it. If you are skilled to an acceptable level in design and installation then your question seems a little odd, but I will try and answer.
• If you use singles then these need mechanical protection and where conduit is used it must be continuous which is hard to do with oval conduit one would normally use round.
• Where flat twin cables are used there is no need for protection although it is common to use capping or oval conduit to reduce the risk of being caught by a plasters trowel.
• Some materials may react with each other and sometimes PVC cables are protected from polystyrene using capping or conduit.
Although you may have someone lined up to do inspection and testing unless they are involved in design and installation they can’t sign for it and could only issue a periodic inspection report not an installation certificate. Without an installation certificate your house will be very hard to sell even if you get the building control to issue a completion certificate.
If the designs are not submitted before the 30 June 2008 then you will need to conform with BS7671:2008 not BS7671:2001.
On a new house cables would normally be fitted before any plaster or plaster board is used in what we call first fix and then all sockets etc fitted after the plastering is complete which we call second fix and since capping is more flush than oval conduit normally capping will be used. Oval conduit is normally used with rewires so narrower channels are required. How either method would produce bulges above your sockets I fail to see?
You admit to not being an electrician and I think you have been lead astray as to what can be completed as DIY and I would recommend you follow the links to Part P in the projects area and pay special attention to the forms it shows from page 23 onwards. Also a look at 17th Edition (Also called BS7671:2008) and changes also link to some parts in projects section then plan and submit you plans to building control and get their reaction the way councils work vary from area to area. Scotland doesn’t have Part P their rules make Part P look easy I am not trying to be a wet blanket but not to make you aware of what is ahead is not really being fair either.

All best Eric
ericmark

Postby ozmondo » Sat Jun 07, 2008 8:23 am

thanks for the reply.

I'll have a chat with my electrician buddy and get him much more involved in everything. Just thought I might save a few bob - ah well!

Just to clarify with the conduit thingy - I was told to use oval conduit [i]without chasing out a channel[/i]. Just lay it flat on the blockwork surface using a few nails either side to keep it straight. The reasons being it [i]might[/i] make it possible to replace the cable in the future without replastering. Also there'd be no chasing out channels to begin with!! The conduit would only be used for drop downs. what do you think??

Anyway cheers for the advice.
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Postby ericmark » Sat Jun 07, 2008 4:08 pm

Yes you can use oval conduit but it is slightly thicker than capping and it will depend on the plaster and how thick he is going to plaster and yes you do stand more chance of reusing the conduit than with capping but even in houses with full metal conduit on a rewire normally all ripped out so does not really help unless very detailed plans are available.
All best Eric
ericmark

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