Either from a switch with Power over Ethernet ports or from an injector placed between an ordinary switch and the unit. What decides it is the Type the access point names on its data sheet, which the source has to offer.
Power and data travel along the same cable, and the whole question is whether the source offers what the device asks for.
Start at the device
The access point’s data sheet names what it needs, in the standard’s own terms rather than in trade names. The Type is the thing to find.
Type 1, defined by IEEE 802.3af, has a source delivering up to 15.4 W at its port and guarantees the powered device 12.95 W. The gap is the run of cable, which dissipates the difference.
Type 2, from 802.3at and printed on packaging as PoE+, raises those to 30 W at the port and 25.5 W guaranteed at the device. It also adds a further classification step by which source and device confirm each other, which is why two units that both say PoE+ can behave differently on a switch that supports only one of the two methods.
Types 3 and 4, from 802.3bt, deliver up to 60 W and 90 W at the port and are the first to carry current on all four pairs rather than two. Each publishes its own, lower, guaranteed figure for the device.
A unit specified for Type 2 will not settle happily on a Type 1 source. Some models start in a reduced mode with a radio disabled or a port unpowered, and the maker states which; others do not start.
Then choose the source
A PoE switch is the tidy answer where more than one device needs power. Read two published figures rather than one: the Type each port offers, and the switch’s total power budget. The budget is what decides how many devices come up, and it is normally well below the sum of the per-port figures.
An injector sits between an ordinary switch and the device and adds power to the cable. It is the right answer for one or two units, and its data sheet has to name the Type — a label saying PoE and nothing else is describing itself rather than a specification.
A proprietary or passive arrangement puts voltage on the cable without the negotiation the standard defines. It is not interchangeable with a standardised source, and connecting a standardised device to one is a way to find out how the equipment maker feels about warranties.
The cabling underneath
The PoE Types name a Category 5e channel or better, and they travel alongside the data, so a powered link still negotiates whatever rate the two ports agree on. The two things share a cable and are decided separately.
Two practical consequences. Length costs power — that is exactly what the two published wattages mean, and a device specified near the upper figure is one to check the run length on. And four-pair delivery puts current down every conductor, so heat rise in a tightly packed bundle is a real consideration addressed by the cabling standards and by how the run is installed.
What to write down before ordering
The access point’s Type and its published wattage. The source’s Type, its per-port figure and its total budget. The length of the run. Five numbers, all published, and together they decide whether the light comes on.
The manufacturer’s own documentation comes first, and this page is not a substitute for it. Every rate, capacity, class figure, endurance rating, port speed and power figure on this page is reported from the manufacturer's own documentation, with its unit written as published, and named as such — none of it is measured here. A stated capacity is reported as the maker counts it, and is never restated in another unit, because the two are not the same figure. And for anything wired to the mains: a UPS and a surge protector are installed, sized and replaced as their own instructions say, and nowhere else. Volt-amperes are not watts, a stated runtime assumes a load the maker names, and a joule rating describes what a protection device absorbs before it stops protecting.
The questions that come up before an order
Can I use an injector that came with a different device?
Only if its own data sheet names the Type and wattage your access point requires. Injectors sold with equipment are sometimes not standard sources at all, and a proprietary arrangement that happens to fit the same socket is not the same thing as a standardised one. The words on the label are not the specification; the Type number is.
Why does my switch power three access points and not the fourth?
Because the per-port class and the total power budget are separate published numbers, and the budget is normally well below the per-port figure multiplied by the port count. A switch that publishes its budget on the data sheet is telling you the number that decides how many devices come up.
Last reviewed 10 September 2026