Short answer: Power over Ethernet (PoE) sends electrical power down the same Ethernet cable that carries the data, so an access point, mesh unit or camera needs only one cable. There are three main versions, and they differ in how much power they can deliver: about 13 W at the device for standard PoE (802.3af), 25.5 W for PoE+ (802.3at), and 51 or 71.3 W for PoE++ (802.3bt). Check what your device needs, then power it from a PoE switch or a single-port injector.
How it works
Two pieces of equipment are involved. The power source is a PoE switch or an injector; the powered device is the access point, camera or other gear at the far end of the cable. The device signals what it needs, and the source supplies up to that amount.
Standard PoE and PoE+ deliver power over two of the cable’s four wire pairs, and PoE++ can use all four, which is how it reaches higher power.
PoE, PoE+ and PoE++
| Name | Standard | Power from the switch | Power at the device |
|---|---|---|---|
| PoE | 802.3af (Type 1) | 15.4 W | 13 W |
| PoE+ | 802.3at (Type 2) | 30 W | 25.5 W |
| PoE++ | 802.3bt (Type 3) | 60 W | 51 W |
| PoE++ | 802.3bt (Type 4) | 90 W | 71.3 W |
Figures from the Ethernet Alliance’s overview of the standards. The device gets less than the switch sends because some power is lost in the cable.
Spec sheets use these names loosely, so match the standard number (802.3af, at or bt) rather than the label.
What your device needs
The device’s spec sheet tells you. Two examples from home equipment show why it matters:
- eero PoE 7 and eero Outdoor 7 need PoE+. eero says standard 802.3af PoE won’t provide enough power for either.
- ASUS ExpertWiFi EBA63 runs on standard PoE (802.3af), or on a 12 V adapter if you’d rather.
A source that supplies more than a device needs is fine; the device only draws what it asks for. A source that supplies less may not be able to power it properly, which is the point of eero’s warning. If you’re not sure, buy PoE+: it covers most access points and cameras at home. Best Wi-Fi access points lists the power each pick needs.
PoE switch or injector?
An injector sits between an ordinary switch or router port and the device, and adds power to that one cable. It’s the simplest answer for a single access point or camera. eero, for example, lists a PoE+ injector or switch, its own PoE gateway, or a weatherproof PoE+ adapter as ways to power the Outdoor 7.
A PoE switch powers several devices from its own ports and saves a pile of power bricks. It’s the better choice once you have two or more PoE devices in the same place, such as a wiring closet feeding ceiling access points and cameras.
Power budget: the number that catches people out
A PoE switch has two limits: the maximum per port, and a total budget shared by every port. NETGEAR’s GS105Pv3, for example, offers up to 30 W on each of its four PoE ports but 63 W in total. Its ports accept both standard PoE and PoE+ devices.
So add up what your devices need and compare it with the total:
- Two PoE+ access points at 25.5 W each need about 51 W, which fits in 63 W.
- Three of them need about 76.5 W, which doesn’t.
How far can the cable run?
The usual Ethernet limit applies: twisted-pair Ethernet is specified for runs of up to 100 metres. Longer runs need a switch or other powered equipment part-way along. For which cable to buy and what speed it supports, see multi-gig Ethernet explained.
Checklist
- Find each device’s PoE requirement on its spec sheet (af, at or bt).
- One device: use an injector of that standard or better.
- Several devices: use a PoE switch and add up their power against its total budget, with headroom.
- Keep each cable run within 100 m.
If you don’t have Ethernet where the device needs to go yet, Ethernet, MoCA or powerline covers ways to get a wired link there.