S.F.U

It is Switched Fuse Unit. It has one switch unit and one
fuse unit. When we operate the breaker, the contacts will
get closed through switch and then the supply will pass
through the fuse unit to the output.

Whereas in Fuse Switch Unit there is no separte switch and
fuse unit. There is only fuse unit which act itself as a
switch. When we operate the fuse unit will close the input
and output of the breaker.
SFU has been used to trip the circuit,particularly for high capacity tripping.
. Where as MCB&MCCB are used for low capacity tripping.