If a PoE injector is used to supply power to the N720, first plug the ethernet cable in N720 and the PoE injector, and then supply power to the PoE Injector.

Explanation: There are PoE Injectors which have too high a switch-on voltage and this voltage can cause damage on N720.

1. First the Ethernet cable is connected to the N720 and injector, then the Injector inserted to the wall;
   
   

   No overshoot 

   
   

2. First the PoE injector plugged into the wall, then N720 connected to the Ethernet cable (most common case)

   

   Overshoot, Vmax > 90V

   The injector has a big overshoot, the voltage goes higher than 90V.