At times, a wire may become shorted, a solenoid valve may get stuck, or dust may cause the electricity to track or to short.
The output fuse protects the output card from this type of problem. The electronics in the card are sensitive and can be damaged easily. The fuse is a method of protection for the output module.
The purpose of the blown fuse indicator is to simplify troubleshooting for a technician. If the indicator is true or on, this means the fuse is blown.
This would lead the technician to the outputs that are assigned or connected through this fuse.
The indicator not only simplifies the task of finding the problem, it also saves the company money by speeding up repair process.
In some situations, a fuse may have more than one output assigned or connected to the fuse.
In other situations each output may have a fuse connected in line with the device. Either is acceptable and may be found in the field.
These methods are usually applied according to the engineer who designed the system at hand.