Which Reference method

[Blacktail]

Hi, designing my first small installation which i will be using for my first assessment with Elecsa/NECEIC etc ( any thoughts on which way to go appreciated). Installation is in an oak wooden framed and mostly glass conservatory with instruction of no visible wiring please! The obvious way of running the majority of the cables is under the floor. Floor construction is concrete pad then approx 100mm insulation 25mm ply, 25mm solid oak boards. Initially was thinking of channelling out top of insulation and running cables under ply/oak . Would 25 mm of ply and then 25 mm Oak flooring be considered a thermally conductive surface (ref 102). Given the nature of the room i can imagine very high ambient temps at floor surface. If i lay cables under insulation, as the builder would prefer due to time constraints, would the pad be considered a thermally conductive surface. It is just conventional poured concrete over compacted hardcore. I guess this will reduce ambient temp factors as well?

 

[sjm]

I would run the cables in 25mm conduit then the builder can pour his concrete on top of this. I think this should make the install method B. You could use a DECENT flexible conduit to speed up installation.

 

[Guitarist]

That's a brave one to do as a first assessment. Not sure if you are planning to feed it through conduit, but I wouldn't dream of just laying T&E under a floor without mechanical protection. As sjm says... if you do, then ref B.

 

[Blacktail]

Thanks Guys for the reply. The concrete pad is already poured. It is on this i was going to lay the cable. On top of this is going 100mm of insulation then 50mm of boarding. I was going to run the cable sandwiched (well actually in a cut out slot) between the concrete and the insulation giving 150mm of total covering to surface hence not considering ducting, but from you reactions think this was a mistake. Table 4A2 No.60 shows multicore in conduit in concrete - Ref B but is stating thermal resistivity not greater than 2K.m/W. If i do it as i have suggested, sandwiched, with one side of the cable/ducting touching the concrete and the other side of the cable/ducting now encased in insulation greater than 100mm i dont think this is B? I was concentrating on Installation methods for T+E in thermal insulation as this seemed most relevant. In which case should i be considering the concrete pad as "the wall". Also if in ducting is it touching the wall? Hope this makes it a bit clearer.

 

[Guitarist]

I can only reiterate that I would not simply lay the cable on a concrete floor with a "notch" cut out of the insulation. Once you put the cable in conduit then you will be creating an air gap around it.
Do you know the thermal resistivity of the insulation which you are planning to cover the cables with?

 

[sjm]

Put the cable in conduit, allow for space factors etc. IMHO what the conduit is then covered with, as regards insulation, doesn't matter and the installation method remains B.

 

[Guitarist]

Put the cable in conduit, allow for space factors etc. IMHO what the conduit is then covered with, as regards insulation, doesn't matter and the installation method remains B.

Have to agree here. Just laying it on a concrete floor, covered in notched insulation would not even be an option in my book.

 

[Blacktail]

Thanks Guys, Ok so we are saying so long as space factors/grouping etc is ok then lay the cable in conduit and treat as method 60 on 4A2 = Ref B. Makes sense. My confusion with that was the the Insulation going on top would have a thermal resistivity greater than 2 K.m/W. The foot note " o " on page 264 states that thermally insulating materials are excluded and as the conduit will be covered on three sides by insulation, thought this would be relevant. The insulation has a thermal conductivity of 0.023 W/m k which im pretty sure is the reciprocal of Thermal resistivity so i am guessing is greater than 2 K.m/W. Sorry for banging on about this but want to get it correct.

 

[Guitarist]

Have you considered notching the insulation on top and laying the conduit above the insulation, rather than below it, under the flooring?

 

[Edd]

Always go on the worst case, If your not sure that it will be classed as thermal insulation then asume it is. The NICEIC will look and see that you have taken the conservative path and your refrence method and calculations can be shown.
If he thinks your method is wrong it will be wrong in the right direction, but you can then ask the questions, and converse with him in the way you were thinking. If you guess the wrong way, then he will rip you a new one. .... Only joking it will be fine