New Build regs on insulation

[Dustydazzler]

20a mcb

Job done

 

[Sean Kennedy]

Hi - its just possible with correct installation method, see diagram for method 102 in Table 4A2 (p390 BBB). But I’ll bet they’re not doing that.
Being a sarky git - I can’t say what this special insulation might be, but it can’t be the thermal insulating kind of insulation then, can it?

Thanks Wilko

 

[Sean Kennedy]

You'll just need to check it complies with reference method 102 and not 103

All cables are in front of insulation. Cheers Matt for the help.

 

[Sean Kennedy]

20a mcb

Job done

Cheers Bro. Thats what I'm going to go with on this one.

 

[HappyHippyDad]

I'm not too sure what the difference is here between 100mm and 140mm of insulation with regards to a wall (not ceiling). A 32A MCB is used for a ring when the parts of the cable route are in a stud wall (ref method 102). It mentions nothing about the depth of the insulation. What it does mention is the U value of the wall being a minimum of 0.1 W/m²K, so the CCC of the cables (in the tables) must be based on the wall having this value.

I have only just had a skim through the net on U values but the building regs state that a wall must have a U value of at most 0.3 W/m²K (lower the value the less heat loss).

Below is an example of a wall with 140mm insulation (not quite the same as the OP's example but I would have thought the U value in the OP's example would be higher as this has a brick wall as well) showing the U value as 0.27,
https://sydenhams.s3.amazonaws.com/Timber Engineering/Downloads/standard-details-1pdf.pdf
so.... criteria for ref method 102 have been met and the CCC of 2.5mm cable will be 21A.

God knows if that's ok for a 32A MCB though as the regs just ignore rings in the CCC tables, but it was fun researching it on a Sunday morning!

 

[Bellendian]

Most timber frames I've been involved with have insulation placed within the wall units, vapour barrier in front of insulation, and then 32mm counter battens to create service void and provide a fixing for plasterboard. In this scenario no cables are running within insulation itself and I wouldn't have any concerns over a 2.5mm ring on 32a breaker.

 

[45140]

…...…..The contracts manager says it's fine. He said its some special insulation.....

And his professional competence and qualification to make that statement is ?????