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Hi all,

I'm not an electrician, just like to understand things for self learning. I was reading about how reference methods will derate the cable. However, either I have some misinformation or I am not fully understanding.

Given the example of twin and earth, inside plastic conduit, buried in a non-insulating wall would be method B? It is derated due to the cable being unable to dissipate heat from to being inside the wall?

If we had twin and earth clipped direct, as the cable is exposed to free air it can dissipate heat therefore method C?

Where the confusion comes is that I am reading that if it was clipped direct but then covered in plaster it would still be classed as method C? That doesn't make sense to me as now we have a scenario more comparable to the inside the wall, it should be classed as method B?

Many thanks
 
Thanks for this but can you explain why? I understand method A being inside a thermally insulated wall would have the largest derating as it's the hardest to dissipate the heat due to it's thermal properties.

I don't understand why method B would have a higher derating compared with C. As C is the one where cables are buried. Unless we are assuming that due to it being a non-insulating wall we are able to dissipate heat in the mass of the wall itself?

Thanks again
 
Thanks for this but can you explain why? I understand method A being inside a thermally insulated wall would have the largest derating as it's the hardest to dissipate the heat due to it's thermal properties.

I don't understand why method B would have a higher derating compared with C. As C is the one where cables are buried. Unless we are assuming that due to it being a non-insulating wall we are able to dissipate heat in the mass of the wall itself?

Thanks again

that's the answer. masonry is non-insulating and so allows for heat dissipation.
 
I don't understand why method B would have a higher derating compared with C. As C is the one where cables are buried. Unless we are assuming that due to it being a non-insulating wall we are able to dissipate heat in the mass of the wall itself?
answer for that is where some cables can dissipate heat in some cables then others .
 
some times Rosco. when you read some of the DIYs on his forum trying to save Moines
putting us sparks out of the jobs .may be they need to read they insurance policy's be for stating any works. if its a spark on here I would help them has much they would help me .
 
In BS7671 there is a list of common installation methods, I think there's 81 listed at present. These are then grouped for use into 6 reference methods from A to F. These reference method groupings have been made after testing and if they are used correctly the cable will not be overheated. Hope that helps :)
 

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