PoE, PoE+ and PoE++ explained: sizing a PoE switch
The differences between 802.3af, 802.3at and 802.3bt, how to calculate the PoE budget a switch needs for cameras, phones and access points, and which cable to use for high-power PoE.
Short answer: add up the maximum power draw of every powered device, add 20% headroom, and buy a switch whose total PoE budget covers it. Check each port class as well as the total: a Wi-Fi 6 access point or PTZ camera often needs a PoE+ (30 W) or PoE++ (60 W) port, not just a PoE (15.4 W) port.
The three PoE standards
| Standard | Common name | Power at the port | Power at the device | Typical devices |
|---|---|---|---|---|
| IEEE 802.3af | PoE | 15.4 W | 12.95 W | IP phones, basic cameras, door readers |
| IEEE 802.3at | PoE+ | 30 W | 25.5 W | Wi-Fi 5/6 APs, PTZ cameras, video phones |
| IEEE 802.3bt Type 3 | PoE++ / 4PPoE | 60 W | 51 W | Wi-Fi 6E/7 APs, LED lighting, thin clients |
| IEEE 802.3bt Type 4 | PoE++ | 90 W | 71 W | Displays, laptops, building controls |
Worked example
A small office with 8 IP phones (6 W each), 4 Wi-Fi 6 access points (20 W each) and 6 cameras (8 W each) draws 48 + 80 + 48 = 176 W. With 20% headroom that is 211 W, so a 24-port PoE+ switch with a 250 W budget is a sensible choice. Remember the switch budget is shared, so a “24-port PoE” switch with a 190 W budget cannot run 24 devices at 15 W each.
Cable matters for high-power PoE
PoE++ pushes current down all four pairs, which heats cable bundles. Use 23 AWG Cat6a or good quality Cat6 rather than thin 24 AWG Cat5e, keep bundles under 24 cables where possible in warm ceiling voids, and always use pure copper, never copper clad aluminium. Use PoE-rated patch leads with proper plug contacts to avoid arcing damage when devices are unplugged under load.
Managed, smart or unmanaged?
- Unmanaged Switches for plug-and-play PoE with no VLANs.
- Smart Switches when you need VLANs for cameras and guest Wi-Fi, PoE scheduling and port-level control.
- Managed Switches for multi-switch networks, Layer 3 routing and full monitoring.
Our PoE switch range lists per-port class and total budget on every product. Use a PoE tester at the outlet to confirm the power actually delivered after installation.