Todays silly question

[down2earth]

Hi,

I need to run some cables from the garage CU to a variety of points hither and indeed yon. As the upstairs of the garage will be used for accomodation there is rockwool 140mm insulation in the gable ends. My question is, can I use some oversized plastic conduit within the rockwool to run cables without having to worry about having to de-rate their capacity, or will I just have to surface mount?

Thanks for any replies

D2E

 

[jimmymac]

If the cable are installed in conduit within insulation the installation reference method would be method A. A de-rating factor would have to be applied. What size cable are to be used?

 

[down2earth]

Only 1.5mm for a light and a switch

 

[Dave 85]

Why on earth are you worried about having to de-rate a 1.5 for a single light?

 

[craigj85]

you only need to consider de-rating factors if the cable in question is covered by insulation for more than 0.5 metre according to 17th edition even if it's in conduit. Have a look at section 523.7 (cables in thermal insulation) of the regs.

 

[kingeri]

Even if you derate by 50%, the cable will still be able to carry enough current safely to supply one light......so what's the issue?

 

[HandySparks]

you only need to consider de-rating factors if the cable in question is covered by insulation for more than 0.5 metre according to 17th edition even if it's in conduit. Have a look at section 523.7 (cables in thermal insulation) of the regs.

BS7671:2008 Amdt 1, has a table 52.2 which shows derating factors for various insulation lengths from 50mm to 400mm. From what I remember, the previous issue also had this (I don't have it to hand).

 

[AndyL]

Hi,

I need to run some cables from the garage CU to a variety of points hither and indeed yon. As the upstairs of the garage will be used for accomodation there is rockwool 140mm insulation in the gable ends. My question is, can I use some oversized plastic conduit within the rockwool to run cables without having to worry about having to de-rate their capacity, or will I just have to surface mount?

Thanks for any replies

D2E

Table 52.2 for cable totally surrounded by insulation a length of between 100mm - 200mm derating factor 0.63
19.5 x 0.63 = 12.28 Amps

So your 1 light on a 6A breaker should be fine mate

 

[craigj85]

Table 52.2 for cable totally surrounded by insulation a length of between 100mm - 200mm derating factor 0.63
19.5 x 0.63 = 12.28 Amps

So your 1 light on a 6A breaker should be fine mate

Where did you get 19.5 from? Is that the length of cable?