Many modern alarm and access control panels make use of PTC fuses. These are resettable fuses that over heat and trip if the current/heat gets above a set threshold. I have seen them used to protect main boards, reader power outputs and so on. PTC fuses generally take a little longer to trip than a standard fuse.
Typically if the power supply is mounted in the same cabinet as a control panel protected by a main onboard PTC, it is acceptable to not additionally fuse power to this device as it is unlikely that any fault could occur that would place load on the power cable or supply.
However if the power supply is remote or there is no main PTC that protects the whole controller/alarm panel it is a good idea to place a fuse at the power supply end. It is important to choose a correct fuse in this case as breaches in security are possible if done incorrectly. I will outline below an example of a fault I found recently.
While upgrading a card reader I accidentally shorted the power wires. I knew the controller protected both the main board and the individual reader outputs with PTC’s so I did not worry too much. Once the new reader was mounted I noticed that there was no power and also no power to any other reader connected to the same controller. Puzzled I checked the panel and was happy to see the installer had used a fuse module however the main panel was fused unnecessarily and with a fast blow fuse.
When I had shorted the reader power the fast blow fuse had popped before the PTC’s had a chance to work taking out the whole controller permanently instead of just a single reader for a short time. This means all an intruder would have to do is short out an external reader to disable the alarm system, they would be free to break in without any alarm or siren event.
In this case no fuse was necessary, if the controller was located remotely to the power supply a higher rated and/or slow acting fuse would have been a better choice to protect against short circuit on the interconnecting power cable while still allowing the PTC’s do their job.