Eli5: How does Ethernet over Power works?

Question

And while we’re at it, how does Power over Ethernet (PoE) works?

Thanks

In: Engineering

Answer 1

For PoE:
The 8 wires in an ethernet cable operate in differential pairs. This means that when you subtract the voltage of one wire from the other, you get the value of the pair. Normally the goal is 1-1=0 or 1-0=1, however, there’s nothing that prevents you from using larger numbers. If you take one of the pairs and increase both wires by 48, you get 48-48=0 and 49-48=1. This means the data can still transfer. You can then use one of the pairs as your 0V (it doesn’t actually have to be 0V because everything’s relative) and another pair as your 48V. The other side can then use those two pairs as their power source while data can still be sent over those pairs. Nowadays there’s active PoE where the devices negotiate the power, but the concept is still the same.