PoE (Power over Ethernet) has three IEEE standards: 802.3af (PoE, Type 1), with 15.4 W at the switch and 13 W at the device; 802.3at (PoE+, Type 2), with 30 W and 25.5 W; and 802.3bt, with Type 3 (60 W and 51 W) and Type 4 (90 W and 71.3 W), using all four pairs. Passive PoE does not follow the standard and can damage unprepared devices.
PoE standards
Power reaching the device is lower than the switch supplies because of cable losses. The standards are backwards compatible: an 802.3bt switch powers an 802.3af device without issue.
| Standard | Common name | Power at switch | Power at device | Pairs | Classes |
|---|---|---|---|---|---|
| 802.3af (Type 1) | PoE | 15.4 W | 13 W | 2 | 0 to 3 |
| 802.3at (Type 2) | PoE+ | 30 W | 25.5 W | 2 | 4 |
| 802.3bt (Type 3) | PoE++ / 4PPoE | 60 W | 51 W | 2 or 4 | 5 and 6 |
| 802.3bt (Type 4) | PoE++ / 4PPoE | 90 W | 71.3 W | 4 | 7 and 8 |
Which type each device needs
Each device’s datasheet gives its PoE type or class and maximum consumption: that is the figure that counts.
| Device | Usual PoE |
|---|---|
| Fixed IP camera | 802.3af |
| Camera with strong lighting, heater or PTZ | 802.3at or 802.3bt depending on model |
| WiFi 6 access point | 802.3af or 802.3at |
| WiFi 7 access point | Usually 802.3at or 802.3bt |
| IP phone and video intercom | 802.3af |
| Displays, mini PCs, LED lighting | 802.3bt |
Passive PoE
Some manufacturers use passive PoE, typically 24 or 48 V, which sends voltage without negotiating with the device. Connected to an unprepared device it can damage it, and a passive-PoE device will not work on a standard PoE switch. Do not mix them and, if needed, use the right injector or adapter.
How to work out the PoE budget
- Add up the maximum consumption of every device the switch will power.
- Check the switch’s total PoE budget covers it with margin, not just per-port power.
- Allow for peaks: camera heaters in winter or infrared at night.
- Respect the 100 m channel; for longer runs, use extenders or fibre.
- With high-power PoE and bundled cables, use good-category solid-copper cable to limit heating.
- Put the switch on a UPS: cameras and WiFi keep working in a power cut.