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.On the Brunel principle I am fitting 30A but I am curious to know.
The rules for cable on a ring, art that each leg must have an as installed continuous current rating of at least 21A. So you could argue that is the minimum rating for any junction also.
Yup 30A sounds like a better plan.
Scott has brought this to us :
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.
Agreed.
Is it "accessible", though? If not, should be soldered and heat shrunk / taped, or crimped.
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.
Logic would suggest that if its a ring its a ring for a reason, but that would mean you would need the big un, but maybe somebody else understands the history of ring mains vs spurs etc. Brian
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. FWIW they are neutral (black) not live cables.
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?
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.
That sounds like it should be fine.
Neutral still carries the full circuit current, so that does not make any difference.
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.
30A and crimping sounds better if you have a crimping tool.
The video shows that the connectors will carry the current when new. But what happens after they have had a few thermal cycles? I would think the wire nut and the choc block will fail first.
Choc block & crimp are gas-tight, so should last. Wago might be gas tight if the wire is never moved, it certainly won't be if any movement occurs. Wirenuts aren't gas tight. US electrical fires are a testament to that.
NT
choc block are not gas tight.
The hole size in a 15 amp choc block is pretty similar to that in a 13 amp socket. And if you overlap the conductors so both screws grip both, I'd say it is going to be just as good as a socket terminal.
If it all fits, I'd use the 30A based on the fuse size. The fuse is there to protect wiring, and 15A seems a bit weedy just in case the ring gets accidentally broken.
Agree. No threaded connector is secure without an *adequate* locking mechanism or sealant. If you look at WW2 electronic stuff, any terminals are lacquered. May not be adequate, but at least they tried. Wagos are supposed to be used with cables retained or clipped down (and in the latter case the box they are in must also be fixed).
yes they are. You're free to go & learn something.
NT
you may like to go inspect the wire ends in some choc blocks then. You'll find the connecting surfaces aren't corroded despite years or decades of service.
rather ambiguous
That does rather depend on if there was adequate screw pressure created when the termination was made. Also on terminations that cycle through a larger temperature range, its not uncommon for terminal pressure to loosen with time.
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