On Thu, 21 Mar 2019 10:54:59 +0000, John Rumm
wrote:

On 21/03/2019 09:59, Scott wrote:
On Wed, 20 Mar 2019 22:08:10 +0000, John Rumm
wrote:

On 20/03/2019 19:15, Harry Bloomfield wrote:
Scott has brought this to us :
I discovered a problem with a join in a ring main and decided to
replace the faulty connector with a terminal block.* I wondered if
this needs to be rated at 30A to correspond with the fuse (RCBO) or if
15A would be okay on the basis that it is a ring and some of the
current will go each way round.

Depending on where on the ring the joint is, and also where the major
loads are, the load may not be shared equally on each leg at the point
of your join. Hence why there is a minimum installed capacity for the
cables themselves of 21A, rather than just half the nominal rating of
the circuit.


On the Brunel principle I am fitting 30A but I am curious to know.

I treat the current rating only as a guide for the cable size they are
able to accept, rather than a rating of the actual connector. I would
happily use a 15amp, providing I could get both cable in and allow them
to overlap, so both terminal screws tighten onto both cables.

That's fair for your traditional chock block style connector, but
possibly less so for wago style ones where the individual wires are
connected only though the connector and make no direct contact with
each other.

It's a choc block. There are three cables in total. One of the
cables runs through both screws. The other two cables come in at
opposite sides. The effect is (a) there is a cable running through to
supplement the connector and (b) each of the other cables is screwed
against the through cable. It's a good tight fit.

That sounds like it should be fine.

FWIW they are
neutral (black) not live cables.

Neutral still carries the full circuit current, so that does not make
any difference.

To clarify: A comes in at the left and goes through both screws, B
comes in at the left therefore in direct contact with A and C comes in
on the right, also in direct contact with A.

In light of this, does the 'leave well alone' principle perhaps apply?

Not really, it sounds like you have a solution that will work well
enough. In reality most terminals you will be able to find that will
take the size of conductors you are using will give an adequate result.

Thanks for your help. I had already done it in the way I described
but I became concerned whether I should change it when I realised the
terminal block was 16A. I'm leaving it as it's very secure with
plenty of surface contact.