How to Use PoE in Your Network

PoE, defined in IEEE standards 802.3af and 802.3at, refers to the ability to provide 54 Vdc (for 802.3at) or 48 Vdc (for 802.3af) operational power through an Ethernet cable from a switch or other device that can provide a PoE-compliant port connection to a powered device (PD). Examples of PDs include:

Ethernet implementations employ differential signals over twisted pair cables. This requires a minimum of two twisted pairs for a single physical link. Both ends of the cable are isolated with transformers blocking any DC or common mode voltage on the signal pair. PoE exploits this fact by using two twisted pairs as the two conductors to supply a direct current to a PD. One pair carries the power supply current and the other pair provides a path for the return current.

Using PoE allows you to operate PDs in locations without local power (that is, without AC outlets). Having such a network setup can reduce the costs associated with installing electrical wiring and AC outlets to power the various devices.