Should I use two fuses for 220V mains?
If you really have a two-phase supply you need two fuses to protect in the event of a phase-chassis internal fault.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1 and 2.

In Figure 1 you need F1 to blow. In Figure 2 you need F2 to blow.

As per the comments, if you don't have two fuses then you need the RCD / GFID to isolate the power. If that doesn't work or isn't there you are depending on the upstream circuit-breaker / fuse which may have a relatively large rating and allow high fault current to flow for some time before tripping out.