What Is PoE (Power over Ethernet) and Which Devices Need It
Basics4 minInnovialabs editorial team
In short
PoE (Power over Ethernet) lets a device receive both data and electrical power over a single twisted-pair cable, so IP cameras, phones and access points don't need a separate power outlet.
PoE in short
PoE (Power over Ethernet) carries electrical power over the same twisted-pair cable that carries data. The power source (a switch or an injector) is called the PSE, and the device that consumes power (a camera, phone or access point) is the PD.
The main benefit: you can mount a device on a ceiling or an outside wall and run just one network cable to it. No outlets, no power adapters and no electrician at every point. The maximum run length is the same as regular Ethernet — 100 metres.
Before turning power on, a standards-based PoE source checks that the device on the other end is actually a PoE device. That is why plugging a regular laptop or printer into a PoE port is safe — power simply won't be applied.
Standards: PoE, PoE+ and PoE++
| Name | IEEE standard | Power at the switch port | Available to the device |
|---|---|---|---|
| PoE (Type 1) | 802.3af | up to 15.4 W | up to 12.95 W |
| PoE+ (Type 2) | 802.3at | up to 30 W | up to 25.5 W |
| PoE++ (Type 3) | 802.3bt | up to 60 W | up to 51 W |
| PoE++ (Type 4) | 802.3bt | up to 90 W | up to 71.3 W |
The gap between port power and device power is the loss in the cable. The standards are backward compatible: a PoE+ device works on a PoE++ port, and a basic PoE device works on a PoE+ port.
Passive PoE (for example, 24 V) is a separate, non-standard option with no device detection. It shows up in budget gear from some vendors. Don't mix it with standard PoE — you can fry a device.
Which devices need PoE
- IP cameras. A basic camera is fine on PoE; PTZ cameras with heaters and strong IR illumination often need PoE+ or PoE++.
- IP phones. Usually basic PoE is enough; models with large screens and expansion modules may need more.
- Wi-Fi access points. Modern multi-radio access points typically require PoE+, and the most powerful ones PoE++. With too little power, an access point may disable some features.
- Access control: card readers, intercoms, electric locks via controllers.
- Other: thin clients, digital signage, sensors, some light fixtures.
Always check the device datasheet for the exact standard and maximum consumption.
The switch power budget
A PoE switch has two limits:
- Power per port — which standard the port supports (af, at or bt).
- Total PoE budget — how many watts the switch can deliver to all ports at once.
For example, 16 PoE+ ports does not mean all 16 can draw 30 W at the same time. If the total budget is smaller than the sum, the last devices to connect simply won't get power.
How to calculate:
- list every device and its maximum draw from the datasheet;
- add them up and keep roughly a quarter in reserve — for camera heaters in winter, new devices and an ageing power supply;
- compare the result with the switch budget, not the port count.
Injectors and splitters
A PoE injector is a small unit that adds power to the line between a regular switch and the device. It makes sense when you have one or two PoE devices and replacing the switch isn't worth it.
A PoE splitter does the opposite: at the device end it separates the cable into data and power for equipment that doesn't support PoE.
With more than a few PoE devices, a PoE switch is usually simpler: fewer power adapters, everything in one rack, and you can reboot a frozen camera remotely by cycling port power.
Common mistakes
- CCA cable (copper-clad aluminium) instead of solid copper: it heats up more and loses more power, especially with PoE+ and PoE++.
- Sizing by port count instead of the total budget.
- Passive PoE on a standard network — a risk of damaging equipment.
- No UPS for the PoE switch. In a power cut, every camera and phone goes dark at once. One UPS on the switch protects them all.