I live in a 20 year old appartment building. The main fuse blew the other
day, and when I replaced it, I noticed that the fuse was a 50A fuse, but
the main circuit breaker is 63A. There was a bag of assorted fuses left in
the apartment when I bought it, and I am wondering if the lower rating
fuse was installed by mistake, since there's very little difference
between the appearance of the 50A and 63A fuse.

Is it normal for the fuse to have a lower rating than the circuit breaker?
I would have thought that the circuit breaker would trip first, and that
the fuse was a final fail-safe.

I have also noticed that the lighting circuit mcb trips everytime one of
the halogen spots in the kitchen, or living room blows. Is this normal?

(I should mention that everything in the appartment is electric, even the
central heating boiler!)

Thanks,

Ro