Reference Method Question

[Alan123456]

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

 

[buzzlightyear]

are you do any work regarding these methods !

 

[Alan123456]

No, as I said simply for self learning and better understanding of how things work and why.

 

[buzzlightyear]

then it is method C for cables buried in walls & method A for cables in conduit buried in thermally insulated wall. method B of cables in conduit mounted on walls .

 

[Alan123456]

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

 

[buzzlightyear]

are you reading BYB !

 

[Alan123456]

Not familiar with what BYB is?

 

[buzzlightyear]

well is a code. all electricians have signed to code of silence only name rank &number will be given.

 

[telectrix]

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.

 

[Rosco]

From that reply buzz is yours captain cop-out 7671

 

[buzzlightyear]

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 .

 

[buzzlightyear]

From that reply buzz is yours captain cop-out 7671

not really .try to give good explanation has best has I can of some methods of installation. this post might get long and winded !

 

[Rosco]

not really .try to give good explanation has best has I can of some methods of installation. this post might get long and winded !

I was only referring to the signed code of silence

 

[buzzlightyear]

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 .

 

[Wilko]

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