I'm planning to fit some two-way light switches in the downstairs
rooms and also some mains powered fire alarms.
The fire alarms will be on their own circuit in 1.5mm^2 3-core and
earth. I don't know how much current a fire alarm uses but I imagine
it's very tiny.
The lights will be 1.5mm^2 T&E. In the grand scheme of things lights
do not draw much current but I suppose its the sum of the lights which
is important. Now even if the radial supplied a dozen 100w bulbs,
that's only 5A out of a possible 16A for the cable (and of course the
MCB is rated at 6A anyway).
Since these cables will carry low current, will they be ok to fit
through the same hole in the joists? I ask because I am paranoid about
drilling too many holes in joists, so the fewer the better. There's
already notching for the CH. OTOH I don't want the cables to overheat
and start a fire. You hear news stories about fires starting from
Is it best to let each ring main/shower/cooker, i.e. big loads have
one cable per load, but allow light loads to share a hole?
- posted 12 years ago