On this page
01. The standards02. Switch vs injector03. Power budget04. See it in a real installation05. FAQ
Power over Ethernet (PoE) sends power and data down the same network cable, so IP cameras, access readers and Wi-Fi access points don't need separate power supplies. A PoE switch powers many devices from its ports; a PoE injector adds power to a single cable. Every switch has a total power budget that limits how many devices it can power.
Key takeaways
- One cable for power and data.
- 802.3af (PoE): up to 15.4 W per port; 802.3at (PoE+): up to 30 W; 802.3bt: up to 60–90 W.
- PoE switch for many devices, injector for one.
- Check the switch's total PoE budget.
- Distance limit is still about 100 m.
01The standards
| Standard | Name | Max at the switch port | Typical devices |
|---|---|---|---|
| IEEE 802.3af | PoE | 15.4 W | Most fixed IP cameras, readers |
| IEEE 802.3at | PoE+ | 30 W | Cameras with heaters/IR, Wi-Fi access points |
| IEEE 802.3bt | PoE++ | 60–90 W | PTZ cameras, larger devices |
The device receives a little less than the port supplies, because some power is lost in the cable.
02Switch vs injector
PoE switch
PoE injector
03Power budget
A 16-port PoE switch doesn't necessarily power 16 cameras at full power. Add up each device's maximum draw (IR on at night uses more) and compare with the switch's total PoE budget, leaving headroom.
Cameras not powering? See NVR not detecting camera and network switch not working.
04See it in a real installation
IP CCTV System Upgrade: Before & After
Before: exposed, weathered cable joints and an old camera on a parapet. After: a tidy IP CCTV system with proper cabling and protected connections.
05Frequently asked questions
Can PoE damage non-PoE devices?
Standards-based (802.3af/at/bt) PoE negotiates before sending power, so it won't power devices that don't request it. Passive PoE injectors are different, so check.
How far can PoE go?
About 100 m, the same as Ethernet. Extenders or switches are needed for longer runs.
Why do my cameras restart at night?
Infrared increases power draw; if the switch's PoE budget is exceeded, cameras can drop or restart.
