A MCB is made up of two sections one will trip without delay at a set overload (normal 5 times marked current with C type) and the other uses heat and takes some time to trip how long depending on amount of overload there are graphs to show time against amount of overload.
the mcbs are B rated.
the hot cupboard has three 12 v spot lights wired into a transformer.
the transformer is rated to 105 .each light is 35 so on the maximum.
we have only tried the spot lights.
could the anwser be something simple.like a break in the wire or a dodgy mcb.or maybe overheating,or maybe has been wired up wrong
Ups my mistake B = x5, C = x10 and D = x20 but that does not really affect your problem a 6 amp MCB tripping on 0.5 amp points to something being wrong I would start with clamp on ammeter but without test gear I can’t think how to progress maybe remove one bulb and see how it goes then!