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.

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.