1
Power at the device: af 12.95W / at 25.5W / bt 51–71W
2
Enough ports is not enough budget: keep 15–20% headroom
3
Reboot loops are usually power, not channels
01 The three standards and their power classes
| Standard | Port output | Power at device | Typical use |
|---|---|---|---|
| 802.3af (Type 1) | 15.4 W | approx. 12.95 W | Standard indoor ceiling or in-wall APs |
| 802.3at (Type 2, PoE+) | 30 W | approx. 25.5 W | Dual-band or high-power APs, some outdoor units |
| 802.3bt (Type 3/4, PoE++) | 60 W / 90 W | approx. 51 W / 71 W | Multi-radio APs, heated outdoor units, PTZ cameras |
These are protocol ceilings; real available power also depends on the switch budget and cable length.
02 How to budget power
- Read the PoE requirement on the AP label (usually 12–25 W); do not size the budget from headline max power.
- Port count is not budget: a 48-port af switch typically provides around 370 W total, which 20 units at 25 W already exhaust.
- Reserve 15–20% headroom for inrush and later additions.
- Cable length: within 100 m on Cat5e/Cat6 the DC drop is acceptable; beyond that, or with thin cable, use a higher grade or local power.
03 Common faults and causes
| Symptom | Likely cause |
|---|---|
| AP reboots in a loop | Insufficient power — an af port feeding a higher-draw model |
| Strange speeds after power-up | Excessive drop across cable or connector |
| One port dead | Port budget already consumed by earlier units |
| Outdoor unit drops in winter | Model below bt power or without heating |
Questions
Q1 Can an af port power an at device?
Not properly. The device may power up but behave erratically or reboot — move it to an at/bt port or use a local supply.
Q2 Can PoE and non-PoE ports be mixed?
Yes. On most switches PoE and data share the same physical port, and non-PoE devices are safe because power is negotiated first.
Related knowledge
PoE Injector vs PoE Switch — Which to Use For a single AP an injector is cheapest; for many points a switch wins. Decide on point count, central management and whether you need multiple VLANs. Default IP Address of Access Points — How to Find It Management addresses differ by vendor and by batch. The reliable approach is not memorising a table but knowing three methods: read the label, read the gateway, or factory reset.
Send us your floor plan and we will return a PoE port and power budget.