Issue link: https://resources.mouser.com/i/1437732
24 Circuit Protection for High-Speed Serial Interfaces Power Over Ethernet PoE describes several standardized or ad-hoc systems that pass electrical power and data on Ethernet cabling. This allows a single cable to provide both data connection and electrical power to various devices such as IP security cameras. Unlike the USB bus, which also powers devices over the data cables, PoE allows for extended cable lengths. Power can be carried on the same conductors as the data or on dedicated conductors in the same cable. In a PoE scheme, the device that receives the power is called the client device or Powered Device (PD), and the device supplying the power is the Power Sourcing Equipment (PSE). Mode A power is supplied over the active data pair found in 10BaseT or 100BaseTX interfaces. Mode B power is applied over the unused pair for 10BaseT and 100BaseT interfaces. For 1000BaseT and 10GbE applications, all wire pairs are used for data transfer, so no spare pairs are available. Figure 3 illustrates circuit protection schemes for PoE Powered Device and Power Supply Equipment. Figure 3: Here, a properly rated transformer and power supply provide the required isolation for IEEE 802.3 compliance. For the PSE, TVS Diodes are used on the specific pair(s) to provide the power. Shown here are 1,500W versions for high-exposure cable and equipment installations. For short cables or installations where lightning exposure is not expected to be high, lower- power 600W or 400W components can be used. For the protection of the PD, both pairs need to be protected as it will not be known ahead of time which pair(s) will provide power. TVS Diodes should be selected based on the expected surge exposure level. (Source: Littelfuse)