Incorrect, filling a fuse body with sand provides additional protection
against arcing in an overcurrent situation.

Glad we got there in the end. The fuse failed to break the current.
The mechanism by which it failed to break the current was that an
arc formed, which is the way fuses which fail to break the current
fail.

We don't know why the fuse operated and failed to break the current.
It may just have expired through old age, or there may have been a
large current flowing for some reason. However, this does not change
the fact that the fuse failed to break the current. If it had broken
the current then there would have been no arc.

Circuit breakers can fail to break the current in the same way. They
can also fail to break the current because the contacts don't move
or don't move far enough.


That is why 'serious' circuit breakers have compressed air blown onto the
gap to suppress arcing.

Jeff