PoE (Power over Ethernet) sends electrical power and network data down the same Ethernet cable, so a device like a security camera or WiFi access point needs only one cable run — no separate power outlet or adapter nearby. A PoE switch or injector supplies the power; the receiving device draws it automatically if it supports PoE, and ignores it safely if it does not.
How PoE Actually Works
A standard Ethernet cable contains four twisted pairs of copper wire. Gigabit Ethernet already uses all four pairs for data, so PoE does not add extra wires — it superimposes DC voltage onto the same pairs data already travels on, using the fact that Ethernet transformers pass DC current through without disturbing the data signal riding on top of it. The switch or injector detects whether the connected device is PoE-capable before ever applying power, through a low-voltage negotiation step, which is why plugging a non-PoE device into a PoE port is harmless — power is simply never sent.
The PoE Standards, and Why the Wattage Number Matters
PoE comes in tiers, each raising the power budget available per port:
- 802.3af (PoE): up to about 15.4 watts supplied, roughly 12.95 W usable at the device after cable loss — enough for basic IP phones and simple cameras
- 802.3at (PoE+): up to about 30 watts supplied, roughly 25.5 W usable — the common tier for WiFi access points and PTZ cameras
- 802.3bt (PoE++ / UPoE): up to roughly 60 or 90 watts depending on type, enough for higher-power access points and some small displays
The practical rule: check the wattage a device actually needs against what the switch port or injector supplies, not just whether both say "PoE." A PoE+ access point plugged into a plain 802.3af port may not power on at all, or may run in a reduced-power mode with features disabled.
PoE Switches vs. PoE Injectors
There are two ways to get PoE onto a cable run. A PoE switch, such as the TP-Link TL-SG1005P or the larger TP-Link TL-SG116P, builds power delivery into every port, which is the cleanest option when several PoE devices — cameras, access points, VoIP phones — all need to connect at once. A PoE injector, such as the TP-Link TL-PoE160S, sits between a regular non-PoE switch and a single device, adding power to that one cable run without replacing the whole switch. Injectors are the cheaper, more flexible answer for adding one or two PoE devices to a network that already has a perfectly good non-PoE switch; a full PoE switch is the better long-term investment once several powered devices are involved, since it also keeps power draw centralized and easy to monitor.
What PoE Is Actually Used For
- WiFi access points: ceiling- or wall-mounted APs are the single most common PoE use case — one cable handles mounting anywhere without an outlet nearby
- IP security cameras: PoE is the standard way to power and network a camera run, avoiding a separate power cable and adapter at every camera location
- VoIP desk phones and intercoms: a single Ethernet drop to a desk phone eliminates its wall-wart entirely
- Small displays, IoT sensors, and some point-of-sale terminals: increasingly powered this way in commercial installs
PoE devices still sit on an ordinary LAN once powered — the power delivery is a physical-layer trick, not a separate network. For the broader vocabulary of how a LAN is structured versus the connection to the wider internet, see What Does LAN vs WAN Mean?
Total PoE Budget: The Number Beyond Per-Port Wattage
A PoE switch does not just cap the wattage on each individual port — it also has a total PoE power budget shared across the whole switch, listed in the spec sheet as something like "total PoE power." Populate every port on a 16-port PoE+ switch with high-draw access points and it is entirely possible to exceed that shared budget even though each individual port is rated for enough power on paper. Larger PoE switches built for camera and access-point deployments budget for this by supplying meaningfully more total wattage than the simple per-port maximum multiplied by port count would suggest is needed, since real installs rarely run every port at its absolute peak simultaneously. When sizing a PoE switch for a project, check the total power budget line, not just the per-port PoE+ or PoE++ label.
Frequently Asked Questions
Can PoE damage a device that does not support it?
No. Standards-compliant PoE equipment performs a detection handshake before ever applying power, and simply will not energize the line if the connected device does not respond as PoE-capable.
Does a longer cable run reduce PoE power delivery?
Yes, to a degree — resistance in the copper causes some voltage drop over distance, which is why standards specify usable wattage at the device end (lower than what the switch outputs) and why the maximum standard Ethernet run of 100 meters (328 feet) also caps PoE runs.
Do I need a PoE switch if I only have one camera?
Not necessarily — a single PoE injector added to an existing non-PoE switch is usually cheaper and simpler for one device. A dedicated PoE switch makes more sense once several PoE devices are involved.
What is the difference between PoE and PoE+?
PoE+ (802.3at) roughly doubles the power budget of the original PoE (802.3af) standard — about 25.5 W usable at the device versus about 12.95 W — which matters for higher-draw devices like modern WiFi access points and PTZ cameras.
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