PoE vs PoE+ vs PoE++: How Much Power Each Standard Delivers

PoE vs PoE+ vs PoE++: How Much Power Each Standard Delivers

The three Power over Ethernet tiers differ mainly in wattage. Standard PoE, defined by IEEE 802.3af, delivers up to 15.4 watts at the switch. PoE+, defined by IEEE 802.3at, delivers up to 30 watts. PoE++, defined by IEEE 802.3bt, delivers up to about 60 watts on Type 3 and roughly 90 watts on Type 4. Some of that power is lost as heat in the copper, so the device always receives less than the switch sends.

Pick the tier by what the device actually draws. A fixed camera or a desk phone is fine on plain PoE. A pan-tilt-zoom camera or a current Wi-Fi access point usually wants PoE+. Heaters, multi-radio access points, and powered displays need PoE++. That is the decision. The rest is the handshake that keeps it safe and the cable math that decides how many of those watts arrive.

What PoE does and the handshake that makes it safe

Power over Ethernet carries DC power and data over the same twisted-pair cable, out to 100 meters. That is the part that changes how you build. A camera or an access point needs one cable and no outlet anywhere near it. You run a single Cat5e or better, and that run does both jobs, with no electrician and no junction box on a soffit twenty feet up. The IEEE 802.3 family of standards is what makes that reliable instead of a fire hazard.

The two ends have names worth learning, because every spec sheet uses them. The switch or injector is the PSE, the Power Sourcing Equipment. The far end is the PD, the Powered Device. The PSE does not just slam voltage onto the pair the moment something plugs in. It runs a detection and classification handshake first, looking for a resistance signature that says "I am a real PoE device," then classifying how much power that device intends to draw, and only then applying full power. The line sits at 44 to 57 volts only after a PD has asked for it.

That handshake is why you can plug a non-PoE laptop or an old unmanaged switch into a PoE port and not destroy it. The PSE never sees the signature, so it never energizes the line beyond the tiny probing current. I have done it by accident plenty of times and nothing smoked.

The wattage tiers, in plain numbers

Here is where the three names diverge. The numbers below are what each IEEE standard specifies at the switch and what is left at the device after the cable takes its cut.

Two things in that table earn a second look. The first is the gap between the switch column and the device column. Plain PoE under 802.3af sends 15.4 watts but the device sees about 12.95. PoE+ under 802.3at sends 30 and delivers about 25.5. That missing chunk is not waste in the device. It is heat dumped into the copper between the two ends, baked into the standard on purpose because the spec assumes a worst-case run.

The second is what PoE++ changed physically. The older tiers, 802.3af and 802.3at, pushed power down two of the four pairs and left the other two for data alone. IEEE 802.3bt powers all four pairs, which is why you sometimes see it called 4PPoE, four-pair PoE. Spreading the current across four conductors instead of two is most of how Type 3 and Type 4 reach 60 and 90 watts without melting anything. More copper sharing the load means less heat per wire.

Backward compatible, until the device browns out

PoE is backward compatible in one direction. A PoE+ or PoE++ switch port will happily power a lower-tier device. Plug an 802.3af camera into an 802.3bt port and it works, because the PSE only ever delivers what the PD negotiates during classification. The big switch does not force 90 watts down a cable to a 12-watt camera. The camera asks for what it needs and gets exactly that.

The reverse is where people get burned. Put a high-draw device on a lower-tier port and it does not get enough power, full stop. There is no negotiating your way to watts the PSE cannot supply. A PTZ camera with an IR illuminator or a built-in heater drops onto an 802.3af port and the symptom is ugly and intermittent. It boots. It runs in daylight. Then the sun goes down, the IR ring fires, the draw spikes past what the port can give, and the camera browns out and reboots. Sometimes it loops. Sometimes it reboots once a night and you spend a week blaming the firmware.

I have chased exactly that where someone fed PTZ domes from an old af-only switch to save a few dollars. Every camera looked fine on the daytime walkthrough. The trouble only showed up after dark when the heaters and IR kicked in. The cameras were not defective. The port could not feed them, and no factory reset fixes that.

Dave's Take: Backward compatibility is the most over-trusted phrase in the PoE world. It is true, and it lulls people into thinking any PoE port powers any PoE device. It does not. It means high ports run low devices safely. It says nothing about a low port running a hungry device, and the failure when you get that backward is not a dead port. It is a camera that works in the showroom and reboots at 2 a.m. all winter. Match the port to the peak draw, including the heater and the IR, not the idle draw.

What you actually need: cameras, access points, phones

Strip away the marketing tiers and this is a draw-matching exercise. Find the peak the device pulls, add the cable loss, then pick the smallest standard that covers it with a little room.

For fixed bullet and turret cameras, VoIP desk phones, and basic single-radio access points, plain 802.3af is usually plenty. These live in the 12-to-13-watt delivered range, exactly what af was built for. You do not need PoE+ for a fixed dome, and paying for it buys nothing.

PTZ cameras change the math because the motor and the IR illuminator are real loads on top of the imager. A pan-tilt-zoom camera with IR, and current Wi-Fi access points that run more radios, sit in PoE+ territory. That is the PoE+ tier from the table above. When in doubt for a camera that moves or sees in the dark, that is the one to pick.

The 802.3bt tier, PoE++, is for the genuinely thirsty gear. PTZ cameras with built-in heaters for cold installs. Multi-radio access points. Video phones with big screens. Some PoE lighting and powered displays. The camera-side tradeoffs get deep, and our PoE security camera teardown walks through what these draws look like on real hardware.

The cable decides how much power arrives

The single thing people underestimate is the cable. Delivered power drops with cable length and with thinner conductors, and the reason is plain physics. The copper has loop resistance. Push current through it and you burn voltage as heat along the whole run, so a long thin cable takes its cut before the device sees a single watt.

That is why the device column in the table is lower than the switch column. The standard reserves headroom for a worst-case run, and making the run worse than that hits the device. Length is the obvious lever, since resistance scales with distance, and a full 100-meter run loses more than a 20-meter one. Gauge is the quieter one. Thin conductors have more resistance per meter, so a cheap cable with skinny copper bleeds more power than a heavier-gauge cable over the same distance.

For long runs or high-wattage devices, reach for lower-AWG Cat6 or Cat6a rather than minimum-spec Cat5e. The thicker copper carries the current with less drop. There is a second-order effect too. Bundled high-wattage runs heat each other up, and warmer copper has higher resistance than cool copper, so a thick bundle of PoE++ cables all pulling hard runs hotter and loses a bit more than the same cables run alone. The gauge and grade you pull is part of the power budget. If you are deciding what to run, the Cat6 vs Cat6a comparison lays out the differences that matter for power delivery.

Dave's Take: "Up to 90 watts" is measured at the switch, in a lab, on a short cable. Read it as a ceiling, not a promise. After 100 meters of real cable you lose several watts to resistance before the device sees anything, and that is by design, not a defect. Spec to the power the device receives, which is the right-hand column of the table, not the headline PSE number on the box. If a vendor only quotes the switch wattage and goes quiet about the delivered figure, that is the answer.

So which PoE switch should you buy

Once you know the tier each device needs, the switch question is about budgets, and there are two of them. People read the first one off the box and get bitten by the second. The per-port maximum is the wattage a single port can deliver, the 15.4 or 30 or 60 number. The total power budget is the sum the switch can deliver across all ports at once, and it is almost always far less than the per-port maximum times the port count. That is the number to hunt for.

So when you size a switch, add up the real peak draw of everything you intend to power and make sure that total sits comfortably under the aggregate budget. Then check the per-port maximum covers your single hungriest device. Both have to pass. A switch that clears the total but caps each port at 802.3at will starve a single 802.3bt heater camera. One with per-port headroom but a thin total budget runs fine until you fill the last ports and it starts shedding power.

Buy headroom too, because devices get hungrier over generations and you will add ports you did not plan for. And buy managed per-port telemetry. A switch that reports actual watts drawn per port is the difference between diagnosing that 2 a.m. reboot in five minutes and chasing it for a week. When a port shows it is pinned at its limit every night, you have your answer without a ladder. These are also the devices you will want to isolate on their own segment, and our explainer on what a VLAN is covers how to fence them off once they are powered and online.

Dave's Take: A "PoE+ 8-port switch" almost never delivers 30 watts to all eight ports at the same time. Eight times 30 is 240 watts, and the power supply inside that chassis is usually nowhere near it. The number that matters is the total power budget, not the per-port maximum, and the marketing leans on the bigger, friendlier per-port figure every time. Ask for the aggregate budget in watts before you trust the label. If the spec sheet buries it or omits it, assume it is smaller than you hoped and size down accordingly.

Get the two budgets right, pull cable heavy enough that the device sees the watts it needs, and PoE is one of the most reliable things you can build. Get the budget wrong and you meet every brownout the standard was written to prevent.

Related: Cat6 vs Cat6a | PoE Security Cameras: Why Power over Ethernet Changes Everything | What Is a VLAN?