Reference Meathod for Timber Frame

[LED Lighting]

Hi All

Just done my first 2 timber frame New build.

What is the reference method for cables installed in Timber frame walls full of insulation >100mm????

 

[Rpa07]

Knowing it was going to be covered with insulation, was any containment considered? Oval, conduit will both greatly improve heat dissipation and should have been factored in with the cable calc design. Who designed the install?

 

[LED Lighting]

didnt need it, its rockwool

I consulted NICEIC and they also confirmed it didnt need anything

 

[Rpa07]

Didn't give you a reference method whilst on the phone, did they? What's your answer from the BS7671 for the method? Table 4A2 has all the stipulations for deciding and the U value of your insulation.

 

[LED Lighting]

Im thinking it 103. No NICEIC didnt say anything because I didnt ask

 

[Rpa07]

Sounds and looks like 103 to me too. Vastly reduces the ccc. Were the sizes correctly selected for the install in your mind?

 

[LED Lighting]

Yes, I was quite happy about it.

NICEIC also confirmed that it was close but just in 32A

 

[Rpa07]

Job done, happy with the install. Anything special about it to show off photos?

 

[LED Lighting]

Not as yet. The first one completed was a garage/workshop.

The 2nd was a family member. I will be taking pictures of that one when Im up there next.

 

[Pete999]

Knowing it was going to be covered with insulation, was any containment considered? Oval, conduit will both greatly improve heat dissipation and should have been factored in with the cable calc design. Who designed the install?

Polite question honestly, are your comments regarding installing the cables in oval conduit and then enclosing them in insulation, the same as you would use for cables in an insulated roof space, or an insulated wall in a normal domestic traditionally built house? because in my humble opinion installing cables in insulation, is a problem but enclosing them in conduit, would this not compound the problem. I have no experience of timber framed houses by the way, maybe I'm missing something?

 

[The Ghost]

Could be 102 or 103 depends if it is touching the wall

 

[Rpa07]

Any movement of air in a problematic space, to increase the dissipation of heat from a cable that is carrying a current in a timber framed house, in my opinion, will improve the longevity and the performance of the cable. 50x50 trunking down a 2.5 metre wall would only help that heat release, again, in my opinion - I'm still learning!

 

[Flanders]

Any movement of air in a problematic space, to increase the dissipation of heat from a cable that is carrying a current in a timber framed house, in my opinion, will improve the longevity and the performance of the cable. 50x50 trunking down a 2.5 metre wall would only help that heat release, again, in my opinion - I'm still learning!

For an example a 2.5mm twin and earth cable in a wall in insulation will take 13.5 amps were as twin and earth in conduit in insulation it will take 20 amps so yes you are correct

 

[Rpa07]

Also I think that if you are involved with the planning stage of the install then this is something that could be implemented and the cost of the containment would be taken up by the savings in CSA of the cable. I may have to remove my rose tinted specs but it seems good practice and safe practice.

 

[HandySparks]

Oval, conduit will both greatly improve heat dissipation and should have been factored in with the cable calc design.

Any movement of air in a problematic space, to increase the dissipation of heat from a cable that is carrying a current in a timber framed house, in my opinion, will improve the longevity and the performance of the cable. 50x50 trunking down a 2.5 metre wall would only help that heat release, again, in my opinion - I'm still learning!

Sure, if you have to run a cable vertically through insulation, then putting it in 50x50 trunking may well allow it to run cooler, but only if the top, and preferably the bottom, are open to the air. Stuffing a piece of T&E in a bit of oval tube isn't likely to make much difference given the limited space available for convection, and may make it worse.

 

[HandySparks]

For an example a 2.5mm twin and earth cable in a wall in insulation will take 13.5 amps were as twin and earth in conduit in insulation it will take 20 amps so yes you are correct

I think the difference here is whether the cable or conduit is touching the (relatively thermally conductive) inner wall or not. Table 4D5 shows that the same cable in insulation but touching the inner wall is rated at 21A.

See also 4A2 for diagrams showing the various possible configurations.

 

[Flanders]

I would say the best design is use method 102 , touching the inner wall surface, that way it looks like the standard cable sizing will still be within tolerance for you standard circuits in a house, but if the op has used method 103 he may have to rate ring circuits to 20amps if he has used 2.5mm twin and earth

 

[westward10]

Polite question honestly, are your comments regarding installing the cables in oval conduit and then enclosing them in insulation, the same as you would use for cables in an insulated roof space, or an insulated wall in a normal domestic traditionally built house? because in my humble opinion installing cables in insulation, is a problem but enclosing them in conduit, would this not compound the problem. I have no experience of timber framed houses by the way, maybe I'm missing something?

I agree Pete I was a bit lost on that, if you enclose a cable in any type of conduit the ccc is further reduced. It ain't going to act as a heat sink is it.

 

[Pete999]

I agree Pete I was a bit lost on that, if you enclose a cable in any type of conduit the ccc is further reduced. It ain't going to act as a heat sink is it.

Well I was a bit skeptical to be honest, Westward 10

 

[westward10]

Well I was a bit skeptical to be honest, Westward 10

I think people worry too much the chance of lighting circuits and ring finals overloading to such a degree in a domestic property because of thermal insulation must be pretty small. I would probably consider shower circuits and the like more of a problem.

 

[Silly Sausage]

Installation methods aside, I think section 523.9 is relevant here.
A derating factor of 0.51 is applicable.

 

[Rpa07]

We are not talking of a particular circuit type here and I agree that lighting and power circuits would not be an issue due to true usage but taking your shower that has a cable route through a full height wall and a little bit more, if 10mm
64amp clipped direct
32amp just stuffed in't middle of it all
44amp in some sort of conduit in't middle of all the insulation.
That's the difference between a nice powerful warm 9.5kw for me and a piddly 7.5 kw for you. There is something in it for fixed loads.

 

[westward10]

We are not talking of a particular circuit type here and I agree that lighting and power circuits would not be an issue due to true usage but taking your shower that has a cable route through a full height wall and a little bit more, if 10mm
64amp clipped direct
32amp just stuffed in't middle of it all
44amp in some sort of conduit in't middle of all the insulation.
That's the difference between a nice powerful warm 9.5kw for me and a piddly 7.5 kw for you. There is something in it for fixed loads.

Am I missing something, how does the ccc increase by 12A because the cable is contained in conduit.

 

[Rpa07]

Look in the tables - it gets reduced from 64 to 44 if contained and in insulation but reduced from 64 to 32 if placed just in insulation. Come on westward did you have a heavy lunch?

 

[Wilko]

Putting on my tin hat, I reckon the good book says no advantage for using conduit in insulation, advantage comes from clipping cable or conduit to the wall. Little pic to illustrate :

 

[westward10]

Okay you are looking at Table 4D5. Your 44A comes from column 7, enclosed in conduit in an INSULATED WALL. Your 32A comes from column 5, in a stud wall with THERMAL INSULATION. Column 7 does not refer to thermal insulation it refers to an insulated wall. None of the Installation Methods in that table refer to cables in conduit surrounded by thermal insulation. Your sums are incorrect.

 

[westward10]

Putting on my tin hat, I reckon the good book says no advantage for using conduit in insulation, advantage comes from clipping cable or conduit to the wall. Little pic to illustrate :

View attachment 33743

Was just looking at the same thing, but it refers to a thermally insulated wall much like column 7 Table 4D5. So from your shown Table you would refer to column 2 in 4D2A which give an amp or so is the same as 4D5.

 

[Leesparkykent]

Okay you are looking at Table 4D5. Your 44A comes from column 7, enclosed in conduit in an INSULATED WALL. Your 32A comes from column 5, in a stud wall with THERMAL INSULATION. Column 7 does not refer to thermal insulation it refers to an insulated wall. None of the Installation Methods in that table refer to cables in conduit surrounded by thermal insulation. Your sums are incorrect.

Yes it does. Column 7 reference method A* for full installation method refer to table 4A2 number 2 but for flat twin and earth cable.

4A2 number 2 multicore cable in conduit in a thermally insulated wall with an inner skin having a thermal conductance of not less than 10 W/m2K c. So you use reference method A to determine CCC.

 

[westward10]

Yes it does. Column 7 reference method A* for full installation method refer to table 4A2 number 2 but for flat twin and earth cable.

4A2 number 2 multicore cable in conduit in a thermally insulated wall with an inner skin having a thermal conductance of not less than 10 W/m2K c. So you use reference method A to determine CCC.

I can see your point but it does not refer to thermal insulation but a thermally insulated wall. Not going to cross swords here my initial confusion was from an earlier post which stated containing the cable in conduit would increase the ccc, and I assume the poster was misguided by Table 4D5.

 

[Midwest]

To add my measly morsel, 7.1 Reference method A, is described as 'wall consists of outer weatherproof skin' etc etc, which suggests to me is for an external wall. Whereas Reference method 102 - 103 are referring to stud walls, and placing in conduit will have no beneficial or detrimental effect to ccc, apart from bunching of cables?

OR should I just carry on cooking me piece of beef

 

[Leesparkykent]

Back to the op If the cables clipped to the stud and covered by insulation then ref method 103. If cable is touching inner wall surface then ref method 102...That's hope its 102.

 

[westward10]

Back to the op If the cables clipped to the stud and covered by insulation then ref method 103. If cable is touching inner wall surface then ref method 102...That's hope its 102.

We are unanimous on that.

 

[Pete999]

We are unanimous on that.

Yes Mrs Slocombe

 

[Midwest]

Beef in. Most of the wood stud work installations I've seen or done have the cables down the middle of said stud work and would never be close to the inner wall surface.

 

[Pete999]

Beef in. Most of the wood stud work installations I've seen or done have the cables down the middle of said stud work and would never be close to the inner wall surface.

No Mate run it in some trunking or conduit that will increase the ccp of the cable.

 

[Leesparkykent]

Beef in. Most of the wood stud work installations I've seen or done have the cables down the middle of said stud work and would never be close to the inner wall surface.

 

[Midwest]

No Mate run it in some trunking or conduit that will increase the ccp of the cable.

Spuds in. You've confused me now Pete, thought the whole thrust of this debate, suggest no benefit of putting cables in conduit in insulated stud wall?

 

[Pete999]

Spuds in. You've confused me now Pete, thought the whole thrust of this debate, suggest no benefit of putting cables in conduit in insulated stud wall?

Trying to be sarcastic, but obviously it didn't work

 

[westward10]

Trying to be sarcastic, but obviously it didn't work

 

[Midwest]

Trying to be sarcastic, but obviously it didn't work

Parsnips in, carrots in & brussels prepped, gravy slowly bubbling. Sorry Pete, got me BS7671 and me 'Fabulous Fanny' cookbook open at the same time, and cough, couple of vinos in. Got it now though

 

[Midwest]

For those interested in my culinary adventure, cauliflower cheese in, braised cabbage in, blackberry up side down cake (her in-doors is doing that), arrrgggh hate Sundays. Wot was the question again?

 

[westward10]

For those interested in my culinary adventure, cauliflower cheese in, braised cabbage in, blackberry up side down cake (her in-doors is doing that), arrrgggh hate Sundays. Wot was the question again?

I am actually in the garden in the October sun, glass of wine with roast lamb on the go.

 

[Leesparkykent]

I went to the local carvery

 

[Midwest]

Cool guys, life too short

 

[westward10]

I went to the local carvery

I do have all the rings and the oven on though. Hey it doesn't matter my cables are in conduit, was a bit worried then.

 

[Leesparkykent]

I do have all the rings and the oven on though. Hey it doesn't matter my cables are in conduit, was a bit worried then.

Yeah I've been worried about banging the shower on since this thread

 

[Pete999]

I do have all the rings and the oven on though. Hey it doesn't matter my cables are in conduit, was a bit worried then.

Are they in insulation as well Westy?

 

[Pete999]

Ive had it thanks I'm gone the insulation is getting to me, as well as the heat, I#m going to thread myself in some oval conduit to make me cooler.

 

[bigspark17]

Could someone give me an example of 102 touching inner surface and how they achived this then?!

 

[Leesparkykent]

Could someone give me an example of 102 touching inner surface and how they achived this then?!

cable in a stud wall in front of insulation.