British 4mm T&E with 2.5mm earth, I've never seen that!
All 4mm T&E I have seen in the UK has a 1.5mm earth.
The usual sizes of British twin & earth cable (6242Y) are as follows:
1.0mm with 1.0mm earth (CPC)
1.5mm with 1.0mm earth
2.5mm with 1.5mm earth
4.0mm with 1.5mm earth
6.0mm with 2.5mm earth
10.0mm with 4.0mm earth
16.0mm with 6.0mm earth
AFAIK 16mm is the largest size of flat twin & earth manufactured.
Note: 2.5mm T&E manufactured between 1970 & 1981 only carried a 1.0mm earth wire.
When the 15th Edition IEE Regs were issued in 1981, it was found that the 1.0mm earth was inadequate for certain combinations of fault current & overcurrent device. The cable standard (BS 6004) was revised & the earth wire incorperated in 2.5mm T&E increased to 1.5mm.
I tend to share Paul Cornwall's view of British T&E cable, it's crap, but considering how cheap it is, what can we expect?
One point in it's favour is that the flat construction enables better heat dissapation, & slightly higher current ratings than round cables of the same CSA.
