Just about to do the final connections at the CU end for my kitchen/
diner refit.

Conundrum: I originally wired this as two rings, one for the left
hand side, one for the right hand side, as there was a pretty heavy
appliance load one side in particular which even with diversity took
up too much of the 32A to leave enough for it to be a single ring.
That was going on the online instructions for the appliances in
question. Then I checked on the telephone, and was told that one of
the built-in ovens needed a 16A supply. So things got shunted around
and the heavy appliance load ended up on a 40A radial to a mini-CU
feeding the ovens via radials.

Anyway, this leaves me with two rings, now massively over-specified.
Which I want to reduce to one ring for that floor of the house, no
point in wasting the CU way, and having a more complicated and less
obvious layout than it now needs to be.

The two rings run different routes back to the CU, when they leave the
dining room they go all the way through a 30ft cellar to the CU. I
can easily intercept them near where they enter the cellar, and
interconnect them so they form a single ring. But that actually makes
the circuit path much longer and is more work than just connecting
them both to the same MCB as a kind of doubled-up ring. The latter
instinctively feels wrong to me, but I can't put my finger on what
would be wrong with it, so I am wondering if I am making work for
myself.

(This is all subject to a building notice and inspection so part p
comments are otiose.)

On 30 Oct, 15:54, John Rumm wrote:
Bolted wrote:
Anyway, this leaves me with two rings, now massively over-specified.
Which I want to reduce to one ring for that floor of the house, no
point in wasting the CU way, and having a more complicated and less
obvious layout than it now needs to be.

The two rings run different routes back to the CU, when they leave the
dining room they go all the way through a 30ft cellar to the CU. *I
can easily intercept them near where they enter the cellar, and
interconnect them so they form a single ring. *But that actually makes
the circuit path much longer and is more work than just connecting
them both to the same MCB as a kind of doubled-up ring. *The latter
instinctively feels wrong to me, but I can't put my finger on what
would be wrong with it, so I am wondering if I am making work for
myself.

If you have four "ends", at your CU and you want one ring, then you need
to join two of the ends to each other[1], and the other two to the MCB.
Then you will have one ring. Take care the overall cable length is not
being exceeded (106m of 2.5mm^2 T&E with 5% allowable voltage drop as
per the 17th edition).

[1] Excuse the egg sucketh comment, but for the avoidance of doubt -
that would be join one end of each ring together, and not both ends of one!

Thanks, I realise all that. If I make it into a single ring I may as
well do that at the other end of the cellar as suggested in my op, to
save 20m or so of unnecessary additional ring length. Circuit length
would be hitting the max otherwise (10m cellar, 8m diner, 6m kitchen,
plus some wiggling around en route x 4).

That's what made me think about the other way, where the circuit path
and voltage drop on either section would be far less.

On 30 Oct, 15:55, Owain wrote:

Connecting 'two' rings to the MCB wouldn't be a standard circuit, also
the MCB terminal might not take 4 x 2.5mm conductors comfortably.

Thanks for the response.

The latter is a point I hadn't considered, the CU and MCB terminals
are pretty generous though.

The non-standard thing is probably enough reason on its own not to do
it, so as to avoid hassle on inspection. I was really wondering why
it should be less preferred than making a single ring which is
effectively twice as long.

If circuit length is not an issue the best way would be to join up two
lose ends to become a single ring.

Other standard circuit would be to split each ring at its far end and
wire the cables as 4 radials off the same MCB - would have to be 20A
though.

It's still got a bit too much load for a single radial (dishwasher,
3kw kettle tap thingy, big extractor hood, couple of fan boosted
radiators, loads of sockets) so sticking with two rings would be
preferable to that.

Unless you are down to your last spare CU way there's nothing wrong
with having the sockets split across a couple of circuits for
convenience.

I've got one spare way, two would be nice. But it's probably the way
to go.

Bolted wrote:
On 30 Oct, 15:55, Owain wrote:

Connecting 'two' rings to the MCB wouldn't be a standard circuit, also
the MCB terminal might not take 4 x 2.5mm conductors comfortably.

Thanks for the response.

The latter is a point I hadn't considered, the CU and MCB terminals
are pretty generous though.

Most reasonably modern kit will take at least 16mm^2 in the terminal on
the MCB. It tends to be older CUs/MCBs/FCs that are more restrictive.

The non-standard thing is probably enough reason on its own not to do
it, so as to avoid hassle on inspection. I was really wondering why
it should be less preferred than making a single ring which is
effectively twice as long.

If circuit length is not an issue the best way would be to join up two
lose ends to become a single ring.

Other standard circuit would be to split each ring at its far end and
wire the cables as 4 radials off the same MCB - would have to be 20A
though.

It's still got a bit too much load for a single radial (dishwasher,
3kw kettle tap thingy, big extractor hood, couple of fan boosted
radiators, loads of sockets) so sticking with two rings would be
preferable to that.

Unless you are down to your last spare CU way there's nothing wrong
with having the sockets split across a couple of circuits for
convenience.

I've got one spare way, two would be nice. But it's probably the way
to go.

Go with two for now, and if you need the spare way later, then combine
them.

--
Cheers,

John.

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"Owain" wrote in message
...
On 30 Oct, 15:29, Bolted wrote:
The two rings run different routes back to the CU, when they leave the
dining room they go all the way through a 30ft cellar to the CU. I
can easily intercept them near where they enter the cellar, and
interconnect them so they form a single ring. But that actually makes
the circuit path much longer and is more work than just connecting
them both to the same MCB as a kind of doubled-up ring. The latter
instinctively feels wrong to me, but I can't put my finger on what
would be wrong with it, so I am wondering if I am making work for
myself.

Connecting 'two' rings to the MCB wouldn't be a standard circuit


But any deviations from BS7671 can easily be noted on any test or
installation certificate.

Common sense does apply.


Unless you are down to your last spare CU way there's nothing wrong
with having the sockets split across a couple of circuits for
convenience.

Two 32A circuits at the CU would be better

Adam