"dave L" wrote in message
m...
HI,

I decommissioned my electric shower so there is nothing attached to
that 30A circuit. I want to add a load of lights to the master
bedroom/ensuite which will (at full load) overload the exsting 5A
lighting circuit. I can't add a new circuit to the consumer unit,
plus the cables exiting the consumer unit are chased in to the plaster
which I don't want to rip out.


How much load are you thinking of taking to run lights ? There is nothing
stopping you from doing what you suggest, but you'd need to replace the
existing fuse with one marked at the new rating. To leave the fuse marked
as 30 amp, but to rewire it with a lower rated fuse wire, is not good
practice.

Is there a good reason not to connect my new lights to the
currently-unused 30A cable? Should I change the 30A fusewire for 5A
if I do connect them? IE, have 5A fusewire connecting to some 30A
cable which connects to 5A cable which supplies approx 1kw max load of
lighting.


When you find out by how much you'll need to run the new lights, then go for
the nearest rating to it. Remember though, that fuse wire only comes in
certain ratings, so you may find that the next one up is not really safe
enough to do the job properly, and you might need to place fused spurs in
line with you new lighting circuits for your own protection.

Also if in the future I upgrade my fusewire consumer unit to one with
MCBs will any decent sparky (i'm wouldn't install the new CU ) refuse
to connect 30A cable to a 6A tripswitch?

Thanks a lot.

A split load consumer unit is now the ideal way of distributing circuits
around the house. Power to sockets is taken from an RCD protected supply,
and lighting is taken from a similar set up as your existing box.