RE: LD10's and MCB's

["James Hoye" <james.hoye@xxxxxxx>]

> I was thinking of putting in say 3 30amp rings (these would be very
> short, running from my fuse board to the board containing the LD10s)
for
> lighting (one for each floor) and running all LD10's into their
> respective 30amp MCB, thus saving on 15 or so 5ampers... good idea?

No problem with the first bit (running 3 x 32A rings) - but the proviso is
that the cable is protected at the main CU with a suitable MCB/fuse.  If
you
want 32/30A then you must use 2 lengths of 2.5mm^2 twin and earth (T&E)
OR 1
length of 4mm^2 T&E.

At the LD10 distribution board, I would be very wary of running the LD10s
straight into a 32A MCB - even though each is fused (at 5A?) in case the
LD10 terminals can't handle 32A (would pose a fire hazard if there was a
short circuit fault insufficient to trip the 32A MCB, but too much for the
LD10s to handle.  Rather I would use an additional CU with several (say 3)
5A MCBs then feeding a bank of LD10s (say 5).  That way you'd only need 3
MCBs (and not 15) - but you would need an additional CU!

The main point to remember is that a MCB or fuse only exists to protect the
wiring from over current caused by a fault.  When going down a cable size
(eg. 4mm to 1.5mm) you must install a suitable protection device between
them.  Going up in cable size poses no problem, PROVIDED that the lower
rated cable is adequately protected.

Lost?  Get hold of
http://www.amazon.co.uk/exec/obidos/ASIN/0852969295/markmccall/
- be safe
and not sorry.

James H