The answer to this and your other posting is that it depends on what is required, whether by client specification, design or safety feature.
To fuse a group of PLC i/p's (inputs), one per slot or module is considered good design. To fuse i/p's individually is not only a waste of space and expense unless determined otherwise, leads to a design point - how do you know whether a fuse has blown or not. Solutions are not straighforward.
PLC o/p's (outputs) are somewhat different. Digital o/p's driving interposing relays or lamps (LED or filament) in good designs are fused in groups. O/p's to direct loads such as solenoids or safety circuits could be individually fused. Blown fuse detection could be achieved:
1. In software by alarms and/or where the process has failed
2. Hardware Fuse blown detection - perhaps the simplest being fuse terminals where an LED illuminates when detecting a voltage across the fuse.
