The standards
| Standard | Common name | Power at the switch port | Power available at the device |
|---|---|---|---|
| IEEE 802.3af (Type 1) | PoE | 15.4 W | 12.95 W |
| IEEE 802.3at (Type 2) | PoE+ | 30 W | 25.5 W |
| IEEE 802.3bt (Type 3) | PoE++ | 60 W | 51 W |
| IEEE 802.3bt (Type 4) | PoE++ | 90 W | 71.3 W |
The difference between the two power columns is what's lost in the cable. Power over Ethernet uses the same 100-meter copper channel limit as data.
Which devices need what
Always check the device's datasheet for its PoE class and maximum draw. As a general guide:
- Desk phones usually run on standard PoE.
- Fixed security cameras commonly run on PoE or PoE+; cameras with heaters, infrared or pan-tilt-zoom motors often need more.
- Modern Wi-Fi access points, especially Wi-Fi 6E and Wi-Fi 7 models, often need PoE+ or higher for full performance. On less power, some run with features turned off.
- Lighting, displays and some outdoor equipment may need 802.3bt.
The PoE budget: where offices get caught
Every PoE switch has a total power budget shared across all its ports. A 24-port PoE+ switch can't necessarily give 30 W to all 24 ports at once. If its budget is, say, 370 W, and you plug in devices that need more than that combined, the last devices either won't power on or the switch will cut power to lower-priority ports.
How to check:
- List every powered device and its maximum draw from the datasheet.
- Add them up and leave headroom for growth.
- Compare to the switch's PoE budget, not its per-port rating.
- Put the switch on a UPS. When it loses power, every phone, camera and access point goes with it.
Running out of PoE budget is a common hidden cause of Wi-Fi problems and cameras that drop offline.
Sources
Technical figures checked against the sources above. Standards and product details change; confirm with the manufacturer for your equipment.
