PoE Budget Planning: How to Power Access Points, Cameras and Phones Without Overloading Your Switch
Power over Ethernet lets one cable carry both data and power to access points, IP cameras, desk phones and door controllers. It saves electrical work and makes devices easy to reboot remotely. It also creates a failure that is easy to miss: a switch that runs out of PoE power will quietly refuse to power, or randomly drop, the last devices that ask for it.
The PoE standards
| Standard | Common name | Power at the switch port | Power available at the device | Typical devices |
|---|---|---|---|---|
| IEEE 802.3af | PoE | 15.4 W | 12.95 W | IP phones, basic cameras, older APs |
| IEEE 802.3at | PoE+ | 30 W | 25.5 W | Wi-Fi 6 APs, PTZ cameras, video phones |
| IEEE 802.3bt Type 3 | PoE++ (60 W) | 60 W | 51 W | Tri-band Wi-Fi 7 APs, multi-sensor cameras |
| IEEE 802.3bt Type 4 | PoE++ (90 W) | 90 W | 71.3 W | Displays, heated outdoor cameras, some room systems |
The gap between the switch-port figure and the device figure is power lost in the cable. Size the switch on the port figure.
Two limits on every PoE switch
- Per-port limit: the highest standard a single port supports, for example PoE+ at 30 W.
- Total PoE budget: the maximum the switch can supply across all ports at once, for example 250 W.
A "24-port PoE+" switch with a 250 W budget cannot run 24 devices at 30 W each, because that would need 720 W. It can run about eight at full PoE+ draw, or many more low-power phones. This is the most common sizing mistake we see.
How to calculate your budget
- List every PoE device and look up its maximum power consumption on the datasheet, not the PoE class it requests.
- Add them up.
- Add 20 to 30% headroom for growth, and for devices that draw more in some conditions, such as cameras switching on infrared at night or heaters in outdoor housings.
- Choose a switch whose total PoE budget exceeds that figure, with enough ports of the right class.
Worked example: six Wi-Fi 6 access points at 18 W, eight IP cameras at 7 W and ten IP phones at 5 W. That is 108 + 56 + 50 = 214 W. With 25% headroom you need about 270 W, so a 250 W switch is already too small. A switch with a budget of around 370 W, or two smaller switches, is the safer design.
Wi-Fi 7 changes the numbers
Tri-band Wi-Fi 7 access points draw considerably more than Wi-Fi 6 models, and some only enable every radio or the full-speed uplink on PoE++. Check the datasheet for reduced-function behaviour on PoE+. Pair Wi-Fi 7 APs with multi-gig PoE++ switching such as the Omada 24-port 2.5GBASE-T switch with PoE+ and PoE++ ports. Our Wi-Fi 7 vs 6E guide covers the rest of the upgrade.
Practical tips
- Use a managed or smart PoE switch so you can see per-port draw and power-cycle a frozen camera or AP remotely.
- Set PoE priority on critical ports, such as access points and door controllers, so they stay up if the budget runs short.
- Put the PoE switch on a UPS. When it loses power, every access point and phone goes down with it. See our UPS guide.
- Use a midspan injector for one or two devices on a non-PoE switch, rather than replacing the switch.
- Use proper cabling. Cat5e works for PoE at standard distances; Cat6 or Cat6A runs cooler in bundles carrying high-power PoE++.
Example switches
- TP-Link Omada 18-port Easy Smart switch, 16 x PoE+, 250 W: small offices with a handful of APs and cameras.
- TP-Link Omada 18-port unmanaged rackmount, 16 x PoE+, 250 W: simple CCTV deployments.
- HPE Networking Instant On 1930 PoE: app-managed, pairs with Instant On APs.
- NETGEAR managed PoE switches: including the AV Line for AV-over-IP.
Frequently asked questions
Can a PoE+ switch power a PoE device?
Yes. PoE standards are backward compatible; the switch supplies only what the device requests.
Why do my cameras reboot at night?
Infrared illuminators raise camera power draw after dark. If the switch is close to its budget, the extra load can push it over. Check the switch's PoE usage at night and add headroom.
What is passive PoE?
Some older or low-cost devices use non-standard "passive" PoE, which can damage equipment that is not designed for it. Stick to IEEE 802.3af, at and bt devices and switches.
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