[FAQ] How does the data signal and power operate in the same Ethernet cable?

There are four total pairs of wires in the Ethernet cable. When the PSE operates in Type 1 and 2 modes, the power signal runs on two pairs of wires while the data signal is injected into either two pairs of wires. For power greater than 30W, all four pairs of wires are used to transmit power. A data transformer is applied to couple data signals onto the wires. On the receiving end, another data transformer will be used to decouple the AC signals from DC power lines. 

Additional Resources

• Learn more about the IEEE802.3bt standard: Power over Ethernet: Getting Started with the New Standard

• Check out TI's PoE landing page: www.TI.com/PoE