@SUNRAY ... I should perhaps have 'spelt out' the implications of the question I asked.....
Throughout this protracted part of the discussion, we have been majoring on the question of whether, because of 'grouping' of cables, 6mm² is adequate for the OP's shower cable.
However, that's only part of the question. Even if the shower cable were 16mm², (if it would fit!) and even if there were only one leg of the ring cable (assumed 2.5mm²) in the conduit (i.e. "2 cables" in total in the conduit), then blind application of Table 4C1 would still result in the conclusion that the situation as a whole was 'non-compliant', since the presence of a second cable (of any description/size) within the conduit would result in the CCC of the ring cable being de-rated to <20A, hence (per explicit regulation) not acceptable as the cable of a ring final.
Kind Regards, John
