Apologies if this has been posted previously. I am currently working
on the outline plan for rewiring a 3 bed semi and have worked through
the calculations for cable size but have clearly missed something as
the resulting cable sizes are far too large. I understand the standard
ring main cable size would be 2.5mm^2 or 4mm^2 depending on load and
whether run through thermal insulation.
Having calculated the required MCB rating of 32A, if corrections are
applied for running in thermal insulation (0.89) and grouping 3 cables
(0.7) this gives a requirement of 51.36A - using the IEE cable size
tables this requires at least a 6mm^2 cable depending on installation
- this can't be right.
Firstly, should I be factoring in the grouping if the cables are only
being grouped for short run in conduit through joists and walls.
Secondly, I must have made a mistake somewhere of not applying some
other factor for it being a ring main - can anyone advise where I
have gone wrong?
Thanks in advance, Simon
- posted 12 years ago