PoE (Power over Ethernet) lets a single network cable carry both data and power, so devices like IP cameras, wireless APs and phones power up the moment you plug in the cable — no separate electrical run needed.

Key takeaways

• PoE is defined by IEEE 802.3af (PoE), 802.3at (PoE+) and 802.3bt (PoE++), delivering 12.95 W, 25.5 W and up to 71 W at the device.

• Standard reach stays at 100 m, the same as ordinary Ethernet; beyond that you need an extender or fiber.

• The switch's total PoE budget — not the per-port wattage — decides how many devices you can actually power.

What PoE Means in One Sentence

A poe switch or injector feeds low-voltage DC over the spare or data pairs of an Ethernet cable, following IEEE 802.3 standards, so a powered device (PD) draws both signal and electricity from one jack.

The Three PoE Power Classes

The table below maps each standard to the real wattage a terminal receives, which is what matters for device selection.

Note: The 12.95 W / 25.5 W / 51 W / 71 W figures are the power at the device. The PSE output is always a few watts higher because cable loss eats the difference.

Reach and Power Budget

A standard ethernet switch with PoE follows the same distance rule as Ethernet: 90 m cable + 10 m patch = 100 m. Past 100 m both the signal and the voltage drop sharply, so you add a PoE extender or switch to fiber.

Power budget is where most buyers miscalculate:

• The number on the spec sheet is the total PoE wattage of the whole switch — say 240 W — and every powered port shares it.

• Each port loses power to the cable: a "30 W" PoE+ port delivers about 25.5 W at the device.

• Rule of thumb: total needed ≈ Σ (device watts ÷ 0.85), then add 15–20% headroom.

Warning: An 8-port full-PoE switch loaded with eight 30 W cameras needs ~240 W+ at the devices. A 120 W model will brown out under full load. Size by the total budget, never by the per-port number.

Where PoE Pays Off

• Surveillance: cameras hang off one poe switch in the wiring closet — one cable, no power socket hunt.

• Wireless coverage: APs draw from the access switch, so corridors and workshops skip per-AP outlets.

• Access & IoT: readers and sensors near power, ideal for spread-out factories and campuses.

• Upside: central UPS keeps cameras live during outages, and you can power-cycle a single port remotely.

Common Misconceptions

"PoE reaches 200 m." Standard PoE stops at 100 m. Long-range claims are either proprietary extenders or 10 Mbps speed drops — not standard PoE.

"30 W means the device gets 30 W." 30 W is the PSE side; the device sees ~25.5 W after cable loss. Size high-draw gear to the PD figure.

"PoE++ is always better — max it out." Buy what the load needs. 4-pair PoE++ stresses cabling and runs hotter; a plain camera is fine on PoE+.

"Passive 24 V/48 V PoE works too." Non-standard passive PoE does no handshake and can fry the wrong device. In industrial sites, use 802.3af/at/bt only.

FAQ

Do I need a special cable for PoE++? No. Cat5e or better carries 802.3bt fine, but the terminations must be solid — 4-pair PoE++ pushes up to 960 mA per pair, so cheap crimps cause heating.

Can I mix PoE and non-PoE devices on one switch? Yes. Standards-based PoE negotiates before supplying power, so a laptop or printer on the same port just gets data.