I am converting a downstairs shower room into a utility room. I've removed
the shower and I now want to install some sockets in the room.
The existing electric shower circuit uses 10mm cable with a 45amp MCB.
Can I use the existing circuit and convert it to a radial circuit for 13amp
sockets, and can i use 2.5mm cable for the rest of the circuit?
Yes. You must swap the 45A MCB with a 32A MCB.
It is very sensible to use the existing 10mm circuit, as it will have low
voltage drop on a circuit expected to take heavy loading. It will prevent
the overloading of an existing ring and minimise disruption to decoration.
No, you must use at least 4mm cable for the rest, and possibly (but probably
not) 6mm. 6mm would be a pain to work with for socket circuits.
If you use 2.5mm, the MCB must be changed for a 20A MCB, which is
insufficient to power the expected loads of a utility room.
Personally I call it a pain in the a**e circuit but it's how my '70s semi is
wired - Large cable from CU to underfloor jointbox then ringed round the
sockets. Figure the sparky got a good deal on the large size cable or was
too idle to pull in the extra leg to the board.
I could see that it has advantages when wiring a tall house. Especially with
current standards as to the number of sockets to install, a 4 storey house
with consumer unit on ground floor could have earth loop impdedence/voltage
drop issues limiting the cable lengths. Running the ring after a length of
10mm could seriously reduce the impact of the initial trunk part of the
circuit on the available length.
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