loft runs

[Tinkler]

A few points that need clarifying regarding loft runs...

Can cables be left running loose over joists and insulation?

Do JBs have to be fixed to something?

If cables are pinned to inside of loft joists and against insulation (4") - does the circuit require de-rating. If so, by how much?

I have no sheathing on the earth wire in the JBs for the lighting circuits(unlike the ring-main) - was this the norm many years ago? If so, has it changed since?

On a different subject...

Can a flex with a rubber socket be attached to a FCU situated in a kitchen base unit so that the socket sits on the floor beneath the unit (runs behind and under) for a washing machine?

 

[securespark]

No. Clip them, and try to avoid the warm stuff.

Yes, preferably.

Yes. 50%, when in contact for more than 500mm.

Yes. Up to 70's a lot of cpc's went unsheathed. Yes, it has changed.

No. See the building regs for advice on where sockets can be located. Basically, if it's at risk of getting wet, its location should be re-considered.

 

[Tinkler]

No. Clip them, and try to avoid the warm stuff.

Yes, preferably.

Yes. 50%, when in contact for more than 500mm.

Yes. Up to 70's a lot of cpc's went unsheathed. Yes, it has changed.

No. See the building regs for advice on where sockets can be located. Basically, if it's at risk of getting wet, its location should be re-considered.

Cheers Securespark..

Regarding the Insulation issue it is impossible to avoid contact with it, particularly as it is the norm now I believe to have 8" of insulation in the loft - the fact that only .5 of a metre is allowed before de-rating leaves nothing to work with really! Running the cable along the top of the joists is an option but that isn't the answer as you have to cross them at some point. Plus having the cable on the top of the joists doesn't make them good for stepping on. Do Insualtion installers actually tell the property occupiers about possible problems with electrical safety - a relative of mine recently had it installed (8") and nothing was mentioned. My property is a single storey with concrete floors with everything running down from the loft; I am seriously considering taking up the insulation.

How does the de-rating work...what needs to be done say for lighting and ring-main circuits protected by 6A and 32A MCBs?

As things stand currently, would my 70s unsheathed earth wires in the lighting circuits and loose JBs and cables fail a PIR?

 

[dingbat]

... it is the norm now I believe to have 8" of insulation in the loft

It's more like 10-12" now!

the fact that only .5 of a metre is allowed before de-rating leaves nothing to work with really!

NO, you start to derate after as little as 50mm! But the good news is that once 500mm is insulated you don't have to apply a factor of greater than 0.5. The unfettered rating of 1.0sqmm T&E is 16A, so your lights are likely to be fine. If you have a shower cable running in the loft then this is more of an issue.

Do Insualtion installers actually tell the property occupiers about possible problems with electrical safety - a relative of mine recently had it installed (8") and nothing was mentioned.

Oh how we laughed! Insulation installers probably don't even know what electricity is. I absolutely guarantee they don't have the faintest idea. And it's not in their interest to put any obstacles in their own way.

How does the de-rating work...

It actually works the opposite way from how most people try to explain it. You start with a design current, select a protective device and apply the correction factors to the rating of the device, then select a cable to cope. So:

Lighting, design current = (say) 4A
Select 6A MCB (next available size up)
Current carrying capacity required = device rating divided by factor (in this case 0.5 for full insulation coverage) = 12A
Select cable. In this instance 1.0 T & E will do the job.

(There is more to it than this, but it gives you the idea)

As things stand currently, would my 70s unsheathed earth wires in the lighting circuits and loose JBs and cables fail a PIR?

Code 2 = needs improvement.

 

[Adam_151]

Yo - http://www.iee.org/Publish/WireRegs...rent_ratings_cables_in_thermal_insulation.pdf

If I'm reading this right, then its saying that depending on how much installation is installed and the way the cable is installed, then sometimes you can assume installation method 15 without further derating factors

 

[Adam_151]

Do Insualtion installers actually tell the property occupiers about possible problems with electrical safety - a relative of mine recently had it installed (8") and nothing was mentioned.

Oh how we laughed! Insulation installers probably don't even know what electricity is. I absolutely guarantee they don't have the faintest idea. And it's not in their interest to put any obstacles in their own way.

Lol, totally true, mate of mine had installation installed, and they couldn't even be bothered to follow the grain of the joists, instead laying it across them, so you couldn't actually see them, in their defence though, they did put a sign up to the effect of "don't try and walk across here" he ended up taking it up and doing it properly himself