Thermal insulation

me1 · Jan 27, 2014

Hi:

I intend to fix some kingspan 25mm (Thermal insulation) to a brick wall.. overall thickness with plaster board will be 37.5 mm.

Then I will be running some cable with in this;with in conduit which will be 25mm diameter (10 meters round about.)
So the Thermal insulation will only be touching two sides of the conduit.

My prob is in table 6b in the OSG gives de-rating factors length of from 55mm = 0.88 to >or equal to 500 mm= 0.50.

I need to work it out for 30 meters of 2.5mm cable and 4mm cable I suspect I will need 4mm or even 6mm.
Where 10 meters of it will be through the king span. Can you help?

Plus what de-rating temperature de- factor would you use this is with in the living room, I have never known it to get above 25 oc.?

benji · Jan 27, 2014

can,t you route it above ceiling or below floor or behind skirting

Spoon · Jan 27, 2014

Table 6B is the old OSG, called F2 (page 141) now. Anyhow thats besides the point. Why cant you use installation Method A (enclosed in conduit in an insulated wall)? or is your thermal conductance too high.

me1 · Jan 27, 2014

benji said:
can,t you route it above ceiling or below floor or behind skirting

It needs to drop down from the ceiling entering the thermal insulation which will be from top to bottom . The floor is concrete.

me1 · Jan 27, 2014

Spoon said:
Table 6B is the old OSG, called F2 (page 141) now. Anyhow thats besides the point. Why cant you use installation Method A (enclosed in conduit in an insulated wall)? or is your thermal conductance too high.

Method A it is. Do I still need to de-rate for the insulated wall, because in table 2.3.1 in the new OSG it says Ref A for 2.5 mm cable needs to be 20A and 4mm 26A

The thickness of the insulation is 25mm

Spoon · Jan 27, 2014

Dont know about your circuit, but you are designing it. Method A only takes into account 'enclosed in conduit in an insulated wall'. ( Read Method A for thermal conductance value) You have to account for all other installation factors.