Power · Networking
PoE
Also known as: Power over Ethernet, PoE+, PoE++, 802.3af, 802.3at, 802.3bt
Delivers DC power over an Ethernet cable alongside data, eliminating the need for a separate power outlet at devices like IP phones, access points, and security cameras.
PoE lets a PoE-capable switch (the PSE — Power Sourcing Equipment) supply power to a connected device (the PD — Powered Device) over the same Cat5e/Cat6 cable carrying data. No power outlet near the ceiling for your access point, no power brick at every IP phone.
PoE standards and wattage
Three IEEE standards define PoE power levels at the device:
| Standard | Name | Max power at PD | |---|---|---| | 802.3af | PoE | 12.95W | | 802.3at | PoE+ | 25.5W | | 802.3bt | PoE++ / 4PPoE | 71.3W (Type 3) / 90W (Type 4) |
Most IP phones and basic APs run fine on 802.3af. Modern dual-radio APs, PTZ cameras, and video conferencing endpoints often need 802.3at (PoE+). High-wattage devices like multi-radio APs, digital signs, and thin clients may need 802.3bt.
Switch power budget
A PoE switch has a total power budget — the maximum total wattage it can deliver across all PoE ports simultaneously. A 24-port PoE+ switch with a 370W budget can support ~14 ports at full 25.5W each, or more ports at lower wattage. When specifying a PoE switch, size the power budget for realistic worst-case load, not just port count.
Injectors
A PoE injector adds PoE capability to a non-PoE switch port — the injector sits between the switch and the device, taking power from a wall outlet and combining it with the Ethernet signal. Useful for adding PoE to a few ports without replacing a switch, but inelegant at scale.