refrence method

[nickblake]

Not if that is loft insulation it would be 101 it's only 103 in a wall and it's not touching the inner wall surface.

Derating values are important and on design of a new installtion or an alteration or addition to an old is paramount. But a common sense approach is in a domestic home is really needed. Apart from a very few circuits ie a fridge, burglar alarm or fire alarm, very few circuits will ever reach critical usage by being on constantly. Lights power and such most likely will never exceed 50% operational hours over a 24 hour period. Of course design and install the most safe and secure installtion but be sensible and use your design experience to the most

It does state 103 table 2.3.1 in the guide to building regs : Surrounded by thermal insulation including in a stud wall with thermal insulationwith cable not touching wall , so if you have a loft thats got 100 of insulation in it with the cables over the top of them then 200mm of insulation on the top then it would be 103

 

[malcolmsanford]

I don't have Part B of the building regs with me Nick so can't comment on them. I would be suprised though when it comes to cable and erection methods they would not go with the same terminology as the BS 7671-2008.

Table 4A2 states that method 103 is for a stud wall, and makes no mention of above a plasterboard ceiling ie loft. As I say I don't have the building regs to hand, but as they are also just a guide, I would rather go with what the BS 7671-2008 guides me to as far as electrical installations are concerned.