All these fuses will say 415V and are generally 100A, although sometimes less. This doesn't mean it's three-phase, unless there are three of them

The 415V is just the voltage the component is rated to €” fuses operate on Amps alone, the voltage is not relevant. A 100A fuse will blow just beyond 100A whether it's at 12V or 1200V.

The same way appliance mains cables are rated to 300V or even 600V; it just refers to the insulation resistance or safety factor of the cable.