Just a quick sanity check - would be grateful if anyone is able to concur as the result is borderline... Ignoring voltdrop considerations and looking only at cable sizing for current - I have been through the regs, Amendment 1 (Green) and concluded, for
2 (plus earth/CPC) unsheathed PVC (70C) single core conductors in conduit, NOT T+E:1) In a brick wall (in brick skin, under plaster, no surface insulation to room, but cavity insulation behind brick leaf) assuming thermal resistivity of brick (inverse-k value) is < 2Km/W:
is Reference Method B, from number 42, page 319
2) In conduit in free air clipped to side of basket tray or laying on joists:Also Reference method B, number 4, page 317.
Basically I'm trying to work out if I can "get away" with 6mm2 rather than 10mm2 for some 40A circuits (cooker, water heater).
To be honest, Ref B gives me 41A at 30C, but I should probably apply a derating factor of 0.87 for 40C as it's a roof space. Then again, it's now an insulated roof so... (Wish I'd put a min/max thermometer in last summer!)
10mm2 is possible (I have 25mm conduit drops) but no sense in pulling heavier cable than I need.The cooker will be a 900mm induction+ovens so 32A is cutting it a bit fine, 40 probably better.
Cheers :)
Tim