Cable De-rating

[rich42]

I am planning to install some 6mm2 SWA down to my workshop. It will be run outside, but in 50mm Square Metal trunking, for 5m then in plastic trunking, buried 400mm down.

Does the cable rating need to be de-rated in this circumstance?

Regards, Rich

 

[conny]

What is the distance from the supply to your workshop and does the cable run through any thermal insulation before exiting the house?

 

[sparxxxx]

Expensive installation, swa does not need any protection and can be buried directly in the ground, trunking is not weatherproof and burying in the ground serves no purpose. Derating per your proposal is not relevant, but check installation method from the power source, as mentioned by conny

 

[333rocky333]

The current carrying capacity of the cable, in the Tables in the regs, take account of the instalation method, reference D is for buried cables and cable ratings drops slightly when buried.
External influences other than being buried may Derate the cable

 

[JohnW2]

The current carrying capacity of the cable, in the Tables in the regs, take account of the instalation method, reference D is for buried cables ....

Indeed. I have to say that I have always been a bit surprised that armoured cable buried in the ground in ducting (Method 70) and buried directly in the ground (Method 72) are both Reference Method D, since in the former case (in ducting) dissipation of heat from the cable will presumably be somewhat less.

In relation to (non-armoured) cables buried in masonry (directly or within conduit), the regs do recognise the ciorresponding difference, since direct in masonry is Ref Method C, whereas in conduit it is Ref Method B (with a somewhat lower CCC).

Kind Regards, John