I am planning on using a tvs diode to clamp power peak to protect network switch; the Port is POE. The issue is that when I measure the voltage of ethernet line to ground, I get around 0.6V. When I use a POE measurement device, its shows the Pin 1,2,3,6 and voltage of 54V. Why can I not get 54V when measuring using Multimeter. Please help me understand.
POE source uses a low voltage/current to detect whether a POE sink is present and how much power it needs before giving power to it, so unless you fake a POE device you don't get voltage. And voltage is between pairs and most likely isolated from ground, so trying to measure against ground will just not work.