M
marsaday
BAS's i will find the correct solution and use the 2.5mm. dont worry yourself too much.
The IEE obviously don't think so or else they wouldn't have put 101 in which has different figures from 103 and which also almost exactly matches the installation method described whereas 103 doesn't.With regard to method 103, although it does mention plasterboard walls, it makes little difference whether it's a wall or ceiling.
Yes, but this is still method 101#......... Table 4A2, BS7671, page 265OP, if you run in a 16A radial in 2.5mm with the cable touching the plasterboard ceiling on one side and insulation atop, this should be OK assuming no other correction factors need be applied.
The IEE obviously don't think so or else they wouldn't have put 101 in which has different figures from 103 and which also almost exactly matches the installation method described whereas 103 doesn't.With regard to method 103, although it does mention plasterboard walls, it makes little difference whether it's a wall or ceiling.
Yes, but this is still method 101#......... Table 4A2, BS7671, page 265OP, if you run in a 16A radial in 2.5mm with the cable touching the plasterboard ceiling on one side and insulation atop, this should be OK assuming no other correction factors need be applied.
You may not like it, but that's what the book says, what are the qualifications of people on this thread to say the IEE are wrong? I shall start, I don't have them.
Ah - but when I started writing my reply to you, marsaday had not written this:Reference Method 101# - the one I used
"above a plasterboard ceiling covered by thermal insulation exceeding 100 mm in thickness"
so the method which applied was not 101#If i remove the old insulation currently between the ceiling joists the cable will be sat on the ceiling below.
It's in a ceiling/under a floor, but the results are the same. Look at para 3 in 523.7 if you don't believe me.Reference Method 103# - the one ban_all_sheds used
"in a stud wall with thermal insulation with cable not touching the inner wall surface"
So is it in a ceiling or in a wall?
That was only half the story - earlier on he said:marsaday said "Is it a no no to lay the ring main under the new joisted floor which will have 200mm of insulation between it."
i.e. it was going to be sitting on insulation with more above it.it will be sat on the ceiling joists and insulation between these joists. Above it will be the new floor filled with insulation.
Only if you conveniently ignore the fact that when you wrote this the derating factor which applied was 0.5.chapeau correct. bas wrong.
No you won't.BAS's i will find the correct solution and use the 2.5mm.
I'm not the one who needs to worry - I'm not going to be at risk because of your incompetence.dont worry yourself too much.
Do you need a picture drawn for you to be able to understand:The IEE obviously don't think so or else they wouldn't have put 101 in which has different figures from 103 and which also almost exactly matches the installation method described whereas 103 doesn't.
I think you have misunderstood me. The point I am/was trying to make is that there is no installation method specifically for flat twin and earth cables, above a ceiling, with cable not touching an inner surface.
I think you have misunderstood me. The point I am/was trying to make is that there is no installation method specifically for flat twin and earth cables, above a ceiling, with cable not touching an inner surface.
Well i don't want to get into an argument with you here simply because the board pedant/thug tried to prove how clever he is and failed.
However, my reading of the OP first post was that he was putting a new room in the loft. The existing joists are there and have insulation between them, below them is (assumed) plasterboard which forms a ceiling. Above the joists, along the top of the joists so to speak,and clipped to the joists, and so above the existing insulation, he will be running his cable. Above this plane, he will be putting additional joists (as is common in loft extensions) which will have insulation between them. Therefore the cable is now between two layers of insulation > 100mm thick and clipped to the existing joists.
This is almost exactly as shown as in 101# on the page I referred to earlier.
What is interesting, is that the current carrying capacity differs from 103#, but mine is not to reason why. I wouldn't have bothered pointing out the difference myself, or defend others, but then perhaps that's just me.
But the end result is as you said, if you want to use 2.5mm, the best way is to put in on a 16amp protective device and run it as a radial.
But after his first post came his second, in which he said "it will be sat on the ceiling joists and insulation ", so why did you decide that meant it wasn't sat on the insulation, but was clipped to the joists?However, my reading of the OP first post was that he was putting a new room in the loft. The existing joists are there and have insulation between them, below them is (assumed) plasterboard which forms a ceiling. Above the joists, along the top of the joists so to speak,and clipped to the joists, and so above the existing insulation, he will be running his cable.
Method 103# demonstrates a cable clipped to a joist. The current rating capacity for any cable is different from Method 101# where the cable is clipped to a joist. If you were to look at the picture examples in 103# and 101# you would intuitively assume that for this method that the current carrying capacity of 101# was less than 103#, whereas it is the opposite.It's because method 101 gives a means for heat to escape - plasterboard and joists are much more thermally conductive than loft insulation.
101# & 103#??Using either method results in the same answer in practice.
Method 103# demonstrates a cable clipped to a joist. The current rating capacity for any cable is different from Method 101# where the cable is clipped to a joist. If you were to look at the picture examples in 103# and 101# you would intuitively assume that for this method that the current carrying capacity of 101# was less than 103#, whereas it is the opposite.It's because method 101 gives a means for heat to escape - plasterboard and joists are much more thermally conductive than loft insulation.
Using either method results in the same answer in practice.
OP, if you run in a 16A radial in 2.5mm with the cable touching the plasterboard ceiling on one side and insulation atop, this should be OK assuming no other correction factors need be applied.
But the end result is as you said, if you want to use 2.5mm, the best way is to put in on a 16amp protective device and run it as a radial.
If you assume this is a ceiling with > 100mm insulation (which it is) then method 101 applies, current carrying capacity of cable is 17amps.
if you assume it is a stud wall (which it isn't) method 102 now applies and the current carrying capacity of cable is 21 amps.
Using either method results in the same answer in practice i.e. it's OK to use 2.5mm cable on a 16amp radial.
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