Surge suppressors are doing their job properly in clamping the CAT 5/6 conductors to ground during surge impulses. A problem that has arisen with the widespread use of GIGE surge suppressors in that they do their job too well. If a surge triggers the surge suppressor, it clamps all the conductors to ground. Since they are all connected to ground they are also all connected to each other. That is the definition of a short circuit. If the circuit is powered with a POE device, it is shorted our every time the surge suppressor is doing its job. In some cases the surge suppressor is the thing causing damage due to this condition.
Many POE devices also contain ESD and surge suppression components to protect their own circuitry. During a surge condition the POE powered device may also short the incoming CAT5/6 cable. Thus blowing the power supply. The POE FUSE will protect both the device and the power supply from damage under these conditions.
Must be installed between POE supply and the surge suppressor device to properly protect the supply.
Fuses are in line with pins 1,2 and 4,5 generally the positive wires of a POE scheme. The LEDs are on 2&5 one one side and 2&4 on the other side. If all 4 wires are energized, 4 leds should be showing. If only 2 or fewer LED are illuminated then generally a fuse is blown. High inrush currents on some equipment will blow the fuses which make them unsuitable in some situations.