How to Calculate maximum power of insulated wire

[jonwestuk]

I am sure it has been asked before and I have looked at a lot of posts before but this is a specific query.

I have just insulated my loft and put boards down and now I have some lighting cables coming through and over the insulation over short runs (all the main electrical runs are in open air running between the roof joists). Therefore the only cable under the insulation are the links between individual down lights, which I have placed within metal insulation guards).

I read on the forum that a 1.5mm Twin earth cable is rated for 3600w. I have also read elsewhere that 60% of the capacity of the cable can be lost if covered within insulation. On that basis the 1.5mm cable used should be good for 1440w?

The maximum power running through a single cable within covered insulation will be 114w as I am using LED 9w Aurora down lights. By my calculations I should therefore be well within the tolerance of the cable that I have used.

Can anyone tell me if I am approaching this calculation in the correct way? Or if my calculations are wrong?

I intend on also asking my electrician who I will have around to rewire my consumer unit in 4 weeks time, however I want to check I am safe in the mean time.

Thx,

Jon

 

[DaftPunk]

As long as the cable is protected by a 6 amp circuit breaker at the consumer unit you'll be fine.

 

[EFLImpudence]

Your figures are incorrect.

For information:
1.5mm² cable has a maximum rating of 20 amps (4,600W @ 230V).
1.0mm² - 16A.

The maximum derating for running through thermal insulation is 50% so, as said, with 6A (1,380W) protection there will be no problem.

 

[jonwestuk]

Your figures are incorrect.

For information:
1.5mm² cable has a maximum rating of 20 amps (4,600W @ 230V).
1.0mm² - 16A.

The maximum derating for running through thermal insulation is 50% so, as said, with 6A (1,380W) protection there will be no problem.

Excellent, thanks so much for your corrections. Glad that I am within quite a safe tolerance