How it works

802.3bt puts power on all four pairs of an Ethernet cable, then classifies how many watts the device is allowed to draw. A power sourcing equipment (PSE) port on a switch or injector runs a detection handshake, then a multi-event classification so the powered device (PD) and the PSE agree on a class. Type 3 PSEs can deliver up to 60 W at the port (Classes up through 6). Type 4 PSEs can deliver up to 90 W at the port (Classes 7 and 8). After cable loss, a Type 3 PD can still see about 51 W and a Type 4 PD about 71.3 W at the far end of a 100 m Cat5e or better channel.

That four-pair path is why people also call it 4PPoE or PoE++. Older IEEE PoE used only two pairs: 802.3af Type 1 tops out near 15.4 W at the PSE (about 13 W at the PD), and 802.3at Type 2 / PoE+ tops out at 30 W at the PSE (25.5 W at the PD). An 802.3bt PSE stays backward compatible with those lower classes. An af-only or at-only switch cannot invent Type 3 or Type 4 watts for a hungry access point or PTZ camera.

Classification is not a marketing slogan. Class 5 and 6 are Type 3 budgets. Class 7 and 8 are Type 4. Dual-signature PDs can negotiate power per pairset. Optional LLDP fine-tuning can trim watts after link-up. Data rates from 1 GbE through multi-gig and 10GBASE-T can ride the same copper when the cable and ports allow it. Power and data share the cable; they are still separate negotiations.

When it matters

It matters when the device on the wall asks for more than PoE+ can give, or when you want one PSE budget that can still feed older PoE gear without a wall wart. Wi-Fi 6/6E/7 access points with radios lit, PTZ cameras with heaters, LED fixtures, thin clients, and some digital signage sit in the Type 3 or Type 4 range. If the datasheet says 802.3bt, PoE++, 4PPoE, Ultra60, or 60 W / 90 W class, match the PSE to that floor. A 30 W PoE+ port will brown out or refuse to power it.

Shopping traps are common. "PoE" on a box can mean af, at, or bt. Budget math matters: eight 60 W ports do not equal 480 W if the switch PSU only has 240 W total. Cable quality matters too. High current on four pairs wants solid Cat5e or better, short enough runs, and a PSE that actually speaks 802.3bt, not a passive injector that just dumps 48 V. For multi-gig desks that also need powered APs or cameras, pair 2.5GbE copper with an 802.3bt budget instead of hoping a PoE+ switch is enough.

Two catalog picks that actually speak 802.3bt: a single-port PoE++ injector for one hungry device, and a rack PoE++ switch when you need many high-watt ports.

The PLUSPOE Gigabit PoE++ Injector (90W) turns one non-PoE Gigabit switch port into an 802.3bt PSE up to about 90 W, with backward support for PoE+ and PoE.

The TRENDnet TPE-BG102g 10-Port Gigabit PoE++ Switch is an 802.3bt switch with eight PoE++ copper ports (up to 95 W each), a 240 W total budget, and two Gigabit SFP uplinks.

The NETGEAR MS108UP Ultra60 PoE Multi-Gigabit Switch mixes four Ultra60 PoE++ and four PoE+ ports on 2.5G copper with a 230 W budget, useful when the desk needs multi-gig and the AP still wants Type 3 watts.

For switching silicon around these PSE ports, read The Best Ethernet Switches for a Faster Home Network. For multi-gig copper that often shares the same closet as PoE++ APs, see Run 2.5GbE to the Desk: Everything You Need. For the radios that push into Type 3 and Type 4 budgets, see What Is Wi-Fi 7, and Should You Upgrade Yet?.