sub mains

[jam2020]

hey guys,

i have to wire 17 new bungalows soon,the DNO meter is in a cupboard about 10 m from the consumer unit. Normally i would just have a 16mm swa suub main with an 80a fuse. trouble is the insulation covering it will be >100mm.reference method 101.my question is what is the current carrying capacity in this case? really dont want to use 25mm if i can help it.

 

[Deleted member 19807]

are you sure the "insulation" is of such a low conductivity that the regulation applies? a lot of loft insulation is so poor that you don't have to derate any cables. its a very grey area and difficult to get conclusive data on but it may be worth doing the research in your case.

 

[jam2020]

im pretty sure it will be the bog standard rock wool stuff all builders seem to use nowadays.i was going to cleet it directly to a joist and tell the site agent to keep the insulation away from it but you know what other trades are like.maybe if i ducted it across the loft space?

 

[andyb]

101 is for twin & earth
Without getting too involved, I would think that with thermal & grouping factors & volt drop you will need at least 25mm.

 

[jam2020]

if i put in cable tray it is in free air and becomes ref method e. current capacity is then 97a. this is looking favorite