Ring mains and consumer unit
 

Hi All,

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
mains?

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.

Dave

Ring mains and consumer unit
 

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 mains?

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.

Taking off the fronts of sockets these appear to be correctly
connected on a ring main.

It is not possible to determine if a radial or ring circuit is in use simply
by examining the connections at the sockets.

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)?

This doesn't make sense at all. I do hope you aren't planning to do any
wiring.

Christian.

Ring mains and consumer unit
 

David wrote:
Hi All,

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
mains?

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)?

If it really is a ring circuit then both ends must come back to the
same 32 amp MCB in the CU.


Possibility 1
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?

Possibility 2
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?

Possibility 3
It really has been mis-wired.


--
Chris Green