PoE Budget Explained: How to Choose a PoE Switch
A PoE budget is the total power a switch can deliver across all its PoE ports at once. To choose a switch, add up the maximum power draw of every device you will plug in, then leave headroom. Eight ports with a 61 W budget and eight ports with a 150 W budget look alike on paper, but only one will run eight Wi-Fi access points.
What PoE does
Power over Ethernet sends power and data down the same network cable, so a camera or ceiling access point needs one cable and no mains socket. The power comes from a PoE switch, or from a PoE injector placed between an ordinary switch and the device.
PoE standards at a glance
| Standard | Common name | Power per port at the switch | Power available at the device |
|---|---|---|---|
| IEEE 802.3af | PoE | 15.4 W | 12.95 W |
| IEEE 802.3at | 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 columns is lost in the cable. A PoE+ port can power a PoE device; a PoE device cannot be given more than its own standard allows. Check what each device needs on its datasheet.
Port power versus total budget
Every PoE switch has two limits: the most any single port can deliver, and the total the switch can supply across all ports at once. The total is the one that catches people out. TP-Link's 8-port Omada switches show it clearly:
| Switch | PoE ports | Total PoE budget (TP-Link) |
|---|---|---|
| SG2008P | 4 of 8, PoE+ | 62 W |
| SG2210P | 8, PoE+ | 61 W |
| ES210GMP | 8, PoE+ | 123 W |
| SG2210MP | 8, PoE+ | 150 W |
For larger jobs, the SG2218P has 16 PoE+ ports with a 150 W budget, and the SG2428P has 24 PoE+ ports with 250 W.
How to work out your budget
- List every device that will take power from the switch.
- Find each one's maximum power consumption on its datasheet, not its typical figure. Cameras draw more at night with infrared on, and PTZ cameras more again when moving or heating.
- Add them up.
- Leave headroom. We suggest planning to use no more than about 80% of the switch's budget, so there is room for a device to be added and for start-up peaks.
- Check every device's PoE standard is supported on its port, and that each cable run is within 100 m.
Worked example: Wi-Fi 7 access points
Six EAP772 tri-band access points, each with a maximum draw of 24.05 W on PoE (TP-Link):
- 6 × 24.05 W = 144.3 W.
- The 61 W SG2210P would run only two of them.
- The 150 W SG2210MP would technically run all six but at 96% of its budget, with no headroom.
- A better fit is a switch with a larger budget, or splitting the access points across two switches.
The EAP772 also has a 2.5G Ethernet port, so a 2.5G PoE+ switch lets it use its full speed. Compare the same job with six EAP653 Wi-Fi 6 access points at 13.5 W each: 81 W, comfortably inside a 123 W or 150 W budget.
Worked example: CCTV
For cameras, take the maximum figure from each camera's datasheet. If eight cameras are each rated at 8 W maximum, that is 64 W: over the limit of a 61 W switch, so a 123 W or 150 W model is the safer choice. Our CCTV kit builder matches cameras, recorders and PoE to each other for you.
When a PoE injector makes more sense
If you only need to power one or two devices from an existing non-PoE switch, a PoE injector is simpler than replacing the switch. Match the injector's standard to the device: an 802.3at device needs a PoE+ injector. For more than a couple of devices, a PoE switch is tidier and easier to manage.
Managed or unmanaged?
Omada smart and easy-managed switches let you see each port's power draw, restart a frozen camera or access point remotely by cycling its PoE, and set VLANs. That is useful on any job where you cannot easily get to the cabinet. See our full range of TP-Link PoE switches.
Planning a TP-Link network? Our network kit builder asks a few questions and puts together a matched kit: Deco mesh Wi-Fi for homes, or Omada access points, PoE switches and a gateway for businesses. We also have kit builders for CCTV, alarms, intercoms and audio.
If you would like a second opinion on a plan before you order, contact our team with a rough floor plan and a list of what needs connecting. We deliver to England, Scotland and Wales, usually within 1–2 working days.
Frequently asked questions
What is a PoE budget?
The total power a PoE switch can supply across all its PoE ports at the same time, in watts. It is separate from the maximum each individual port can deliver.
What happens if I go over the PoE budget?
The switch will refuse power to, or switch off, the lower-priority ports once the budget is used up, so some cameras or access points will not come on or will restart.
Can a PoE+ switch power a standard PoE camera?
Yes. PoE+ (802.3at) ports are backwards compatible with standard PoE (802.3af) devices; the device only draws what it needs.
How much headroom should I leave on a PoE switch?
We suggest planning to use no more than about 80% of the total budget, so there is room for added devices and start-up peaks.
Written by the team at Zenith Security Co., a security and networking supplier based in Wolverhampton and trading since 2012. We supply equipment and do not install it; depending on your requirements and your area, we can point you towards a qualified trade installer. Product figures in this article come from TP-Link's published specifications as listed on our product pages.
