Cables in Timber frame extension

[jonesyt]

HiDIYnot : Building a 5x7m single story extension : Can someone please tell me the building regulations for running a 2.5mm ring mains circuit thru the 140mm slab insulation within the 140mmx 47 mm stud walls . Is it ok just to tack the cable to the stud work or does it have to run in plastic conduit or other ?
Thanks V much , TimfromCornwall

 

[PrenticeBoyofDerry]

You will have de-rating due to the insulation within the stud work this will reduce current carry capacity of cables.

If the cable is clipped to stud so it is touching the inner surface of the plasterboard you will be looking at a current capacity of 21A for circuit.
If not touching inner surface 13.5A capacity.
If run in conduit 20A capacity.
Also cables must be routed in permitted safe zones.
http://www.diynot.com/wiki/electrics:installation_techniques:walls
and have RCD protection.

 

[jonesyt]

Thanks for that info DSS ,so in practice the building regs dont stipulate running in conduit ? Just fit appropriate rated RCD ?as per your info

 

[PrenticeBoyofDerry]

The wiring regulation (BS7671) are more concerned with the electrical requirements, such as method of selection and erection, general characteristic, protection of circuits, current ratings etc..
Building regulation will be concerned with electrical and structural safety. They won't tell you how this is reached, that is when you turn to BS7671.

 

[jonesyt]

many thanks DSS , all interesting stuff : I will need to get a NICE IC ? SPARKY to sign it off in the end anyway so Ill confirm specs with him , its only a bedroom so probably an electric blanket or two :0 , cheers Tim

 

[riveralt]

many thanks DSS , all interesting stuff : I will need to get a NICE IC ? SPARKY to sign it off in the end anyway so Ill confirm specs with him

 

[ban-all-sheds]

I will need to get a NICE IC ? SPARKY to sign it off in the end anyway

The phrase "it doesn't work like that" is often apposite.

$64,000 Q: When you applied for Building Regulations approval, what did you say, or what did you by default allow to be assumed, would be the way you would ensure that the electrical work would comply with Part P?

If, by commission or omission, you said that it would be done by a registered electrician then your plan of DIYing and "getting it signed off" needs changing before it's too late.

 

[JohnW2]

If the cable is clipped to stud so it is touching the inner surface of the plasterboard you will be looking at a current capacity of 21A for circuit. If not touching inner surface 13.5A capacity. If run in conduit 20A capacity.

Those are indeed the figures in Table 4D5, but I've never quite understood why "in conduit in an insulated wall" (Method A) has so much higher a CCC than 'in insulation within wall, not touching inner surface' (Method 103) - since, in terms of that description of Method A, the conduit might be totally buried within the insulation and therefore, particularly if the conduit wasn't significantly ventilated, seemingly thermally not much different from Method 103.

In fact, the footnote to 4D5 for Method A refers one to Method 2 in Table 4A2 and, although the description there says nothing about this, the diagram shows the conduit in contact with the inner surface of the wall. If that were the case, I could understand why Method A would be similar to Method 102, rather than 103 - but I see nothing anywhere saying that the conduit has to be touching anything. Am I mising it?

Kind Regards, John.

 

[jonesyt]

my word , what Pandoras box I have opened , Ok simple question , has anyone ever carried out a 6 x twin 13 A socket electrical installation on a timber frame bedroom extension ( 140 x 47 studs , slab ins' infill , 27mm thermaline plasterboard ) and if yes please could you enlighten the forum on the simplest method ? Thanks Tim from Cornwall

 

[riveralt]

my word , what Pandoras box I have opened , Ok simple question , has anyone ever carried out a 6 x twin 13 A socket electrical installation on a timber frame bedroom extension ( 140 x 47 studs , slab ins' infill , 27mm thermaline plasterboard ) and if yes please could you enlighten the forum on the simplest method ? Thanks Tim from Cornwall

The answer to the first part of your question is yes.
The point that you seem to be missing or ignoring is that the electrical work you are doing requires notification to your Local Authority Building Control.
This notification may have been completed by yourself as part of the planning application, but there will be a requirement for you to present to the LABC inspectors a Building Regulation Compliance Certificate in order for them to sign off the extension.
Doing the electrical work yourself is fine except that you will be required to provide the LABC with evidence of compliance with the building regulations , Electrical certification and test results for example.
If you have the testing equipment and appropriate certificates and know what you are doing then you can complete the lot yourself.
However, based on the questions you are asking here it appears that you do not know the difference between the Building Regulations and BS7671 nor have the general knowledge to comply.
Furthermore, no self respecting electrician (at least those who are registered with a competent persons scheme) can lawfully come in at the end and sign the Electrical Installation Certificate to say he designed, installed and tested the installation.
So you must ask him, not us, how he wants the cables to be run and the especially the cable sizes, given the insulation issues.
Pandoras box no, commonsense yes.

 

[jonesyt]

thanks River , I assumed there was a standard procedure for installing six sockets on a timber frame extension , the building control is happy for a DIY install as long as they get the cert' from the sparky , he will check for compliance of course . Cheers

 

[ban-all-sheds]

There's no guarantee that he can DIY, even with the involvement of an electrician, hence my question. It's possible that even if he was a qualified electrician (but unregistered) he would not be allowed to do it.

Jonesy - if your LABC are expecting the work to be done by a registered electrician then that's what must happen - you doing it and "getting it signed off" will not work. Or you need to go back to them and get an amendment made to your application & their approval.

If they are happy for you to DIY and provide inspection and testing results from an electrician then you have to find an electrician prepared to do this, you have to agree with him exactly what you will do, and you have to have every single design and installation query answered by him - nobody else. And you have to find that electrician right now, before you do a single thing regarding the electrics.

You cannot ignore this issue - if you do then you could well end up, as others have done, with your LABC refusing to give you a Completion Certificate.

 

[ban-all-sheds]

Our posts crossed.

The only person you can ask these questions of is your electrician.

 

[PrenticeBoyofDerry]

if yes please could you enlighten the forum on the simplest method ? Thanks Tim from Cornwall

Radial circuit 4.0mm cable on 20A MCB, run in conduit.
You are using thermaline boards, so the contact area of the cable will not avoid insulation.
But as stated talk to the electrician you have assigned to inspect/test and cert work.

 

[jonesyt]

thanks DSS : thats a result 4mm /20 A /conduit , also Ill probably cut out routing channels in the THERMALINE backing
so the cable has a chance to diffuse heat with outside world for when I get that Hadron Collider machine hooked up to the bedside lamp !! best Tim