what size fuse 450 hd

[aussie]

hi everyone what size fuse should i use in line with my hook up wires as from the factory my palomar 450 hd never had one. i have been using a 30 amp fuse but some these times blow. i think amp may have a fuse in side ? if so do i need to use a fuse in line on power wires . thanks guys & gals damien