Power over Ethernet (PoE) delivers electrical power alongside data over standard twisted-pair cabling. The IEEE 802.3 standards define how much power the PSE (power sourcing equipment — usually a switch) supplies and how much the PD (powered device) can actually use after cable losses.
Standards at a glance
| Standard | Name | Type | Max PSE power | Max PD power |
|---|---|---|---|---|
| 802.3af | PoE | Type 1 | 15.4 W | 12.95 W |
| 802.3at | PoE+ | Type 2 | 30 W | 25.5 W |
| 802.3bt | PoE++ | Type 3 | 60 W | 51 W |
| 802.3bt | PoE++ | Type 4 | 90–100 W | 71.3 W |
The PD always gets less than the PSE supplies — the difference is lost as heat in the cable. Plan against the PSE figure (switch budget) and the device’s rated draw.
Power classes
| Class | Type | Max PSE power | PD power range |
|---|---|---|---|
| 0 | 1 | 15.4 W | 0.44–12.95 W |
| 1 | 1 | 4.0 W | 0.44–3.84 W |
| 2 | 1 | 7.0 W | 3.84–6.49 W |
| 3 | 1 | 15.4 W | 6.49–12.95 W |
| 4 | 2 | 30 W | 12.95–25.5 W |
| 5 | 3 | 45 W | up to 40 W |
| 6 | 3 | 60 W | up to 51 W |
| 7 | 4 | 75 W | up to 62 W |
| 8 | 4 | 90–100 W | up to 71.3 W |
Practical notes
- Budget is per-switch, not per-port. A switch with many PoE ports rarely powers them all at maximum simultaneously — check the total PoE power budget.
- Cable matters. Longer runs and thinner conductors (e.g., CCA cable) increase loss. Keep runs within 100 m and use quality Cat5e/Cat6.
- Type 3/4 use all four pairs. PoE++ (802.3bt) powers over all four pairs; older Type 1/2 use two.
Related
Use the PoE Calculator to add up device draw and check it against your switch’s PoE budget.