Welcome seattleman.
You can use a non-fusible disconnect on any load that the correct overcurrent protection is already installed.
Say a HVAC unit that has the correct overcurrent protection at the panel, why spend extra money on a fusible switch and fuses, this can be a lot of money when it is a large 600 volt rated switch and fuses.
You may use a fusible switch any place that a non-fusible switch is presently installed and you can even get "non-fuse" 'fuses' for the switch.
These are UL listed devices to make a fusible switch non fused.
Bob
