Andrew Barber asks whether there are any calculations that he can apply to a cable in contact with a plywood ceiling having loft insulation to obtain a more accurate current carrying capacity value? His question is answered by the ECA (Theme - Installation Tips):
Question: Table 4A2 Reference Methods 100,101,102,103 talk about thermal insulation having a minimum U value of 0.1W/m2K.
I'm carrying out a periodic inspection and test on a new home, with the cable touching a plywood ceiling having the insulation in contact with the cable on three sides 150mm thick, Reference Method 101. The loft insulation has a U value of 0.17 W/m2K.
Are there any calculations I can apply to the cable for a more accurate current carrying capacity?
This is other than applying an incorrect Reference Method to obtain overload protection on a ring main wired in 2.5mm2 to pass, which I've been advised to do by the home's manufacturer.
Answer: There aren't calculations you can easily apply. The cables would have to be tested using that value of thermal insulation to produce a different current carrying capacity value.
I doubt very much that it would make enough difference to make this circuit comply. Basically, if you are installing a 32A ring using Reference Method 101, 2.5mm is too small.
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