In my house there is a consumer unit with RCD. It has 5 circuits on it
(1 cooker, 2 ring mains, 2 lighting). Taking off the fronts of sockets
these appear to be correctly connected on a ring main. However, I can
only see 5 wires going into the consumer unit - I would have thought
there'd be 9, assuming that both sockets and lighting were on ring
Am I being an idiot? Why would anyone bother wiring up sockets on a
ring main and then not complete the ring back at the consumer unit? Or
is it possible for example for only the 'live' ends of the ring to go
to the consumer unit, with the other 'earth' end of the ring being
connected to the main supply (where I can't see it)?
Thanks for any ideas.
Firstly, lighting circuits are almost never run in rings, but in radials.
Radial circuits are ones that run in a tree like fashion, branching wherever
is convenient. (They don't have to branch, if they don't want to).
Socket circuits can be run in rings OR radials. However, standard 2.5mm
cable is not suitable for running a 32A socket circuit in a radial. Thicker
cable must be used (usually 4mm or 6mm, depending on details) or the circuit
derated to 20A.
I suspect that either your house is wired using radial circuits, or that
extra cables enter the consumer unit concealed from behind.
It is not possible to determine if a radial or ring circuit is in use simply
by examining the connections at the sockets.
This doesn't make sense at all. I do hope you aren't planning to do any
If it really is a ring circuit then both ends must come back to the
same 32 amp MCB in the CU.
Are you sure the socket circuits are supposed to be ring mains? It's
not mandatory you know and there are perfectly acceptable alternatives.
Are the MCBs on the socket circuits 32 amp?
Are you sure you can see all the wires coming out of the CU? There
may be some going straight back into the wall it's mounted on. Have
you taken the cover off the CU to see how many wires go into each MCB?
It really has been mis-wired.
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