getting a grant for DIY loft insulation

[geoff]

In message , ARWadsworth writes

According to Mr Lee's statement, yes, every one

[Alan Braggins]

Technically there will be a point where it is true - beyond the point where the body heat of the occupants is enough for all heating needs, further insulation will have no additional benefit, but there will still be a carbon cost to making and installing it though.

[Dave Liquorice]

10A *in air*. What factor do you derate by for "under insulation" 50% springs to mind but it could well be more...

[Duncan Wood]

It's a non trivia question, although in anything which doesn't have electric heating normally irrelevant.

[Phil W Lee]

PeterC considered Mon, 13 Apr 2009

08:16:33 +0100 the perfect time to write:

Until someone comes along and wires ouside security lights to the lighting circuit, because the cumulative load is still under the free-air load specification of the wiring. Until the wiring isn't in free air anymore. Oops.

[Dave Liquorice]

Rubbish. ICBA do dig out the actual figures but in this example of a cable rated at 10A in free air and a 50% derating in insulation the load that the cable is now capable of carrying "safely" is only 5A. But it is "protected" by a 6A MCB. Which, remember, will carry 6A indefinately and won't trip at 6A. Again ICBA to find the figures but 10% overload to trip in less than say 10 mins seems reasonable so that nearly 7A before the protection activates. If the protection is a fuse then look at currents in the order of more than 15A before the fuse blows in less than 10 mins.

And that "safe" 5A is only 1150W, which is not a great load for a lighting circuit.

[Duncan Wood]

Of course if you could be arsed or knew what you where talking about then you'd have started with 15A derated by 50% or 19.5A derated by 50%. However you also need to know how hot it's likely to be etc. The design figures are for the MCB rated current, not the actual current.

[Duncan Wood]

Of course you'd have to fail to notice the insulation & if you're that dumb you shouldn't be playing with the electricity.

[Mike]

What if no carbon is used in the manufacture and supply of the insulation nor in heating the location that is being insulated?

[PeterC]

The cable under insulation is 1.5; the 1.0 is about 6' higher up and has a total load of 77W of CFLs, so about 150VA - should be OK.

The buried cable has a total load, everything on, of about 500W and of course there's v. little of the cable taking that.

Having seen 2.5 'running' an electric shower and the amount of insulation stuck to it, I know what can happen.

[geoff]

In message , Mike writes

Well, since he's not even man enough to attempt to justify his statement

- we can't even guess where his head's at

[magwitch]

Yeah as in sheep wool.

[Phil W Lee]

"Duncan Wood" considered Tue, 14 Apr 2009

10:30:40 +0100 the perfect time to write:

The point is more that the insulators should be checking the maximum load of the cables they are about to bury before doing so, but they aren't electricians, so don't.

[Phil W Lee]

Mike considered Tue, 14 Apr 2009 11:59:34 +0100 the perfect time to write:

Then you're looking at a thatched cottage, with reed-beds at the end of the garden.

[dennis]

What's wrong geoff, upset that someone else knows what I said was true but you had already put your foot in it again. Maybe you should stick to capacitors or was that contacts?

[dennis]

If the insulation was perfect the derating would have to be 100%. The 50% figure is just a figure used so that electricians can get on with their work. An engineer could actually work out what the real figure was if it was necessary.

I don't know what the 50% is based on but I don't expect they considered 1m of insulation around a cable so be careful if you have one of those new super insulated houses with far too much insulation in them.

[Duncan Wood]

If you run an electrical cable in an attic then it's only sensible to assume it may be buried. Fortunately if it's on a 6A MCB it'll be fine.

[Duncan Wood]

Nope, the cables's a conducter :-)

[dennis]

You don't need that much insulation for it to be true. Take the current standard of 300mm.. its going to save about 99.9% of heat lose through it. Adding another 300mm will double its resistance to heat and it will save you

99.95%. It doesn't take much to realise that spending the same amount of carbon to save .05% of the energy is starting to look ineffective.

[dennis]

Do you have an example?