This article explains the differences between these products from four perspectives: power, cable pairs, compatibility, and application scenarios.
First, here is an overview of the evolution of the PoE / PoE+ / PoE++ standards and their key parameters:
IEEE 802.3af (PoE) — First-generation standard
Released in 2003, it provides a maximum power output of 15.4W, with 12.95W available to the powered device. It operates within a voltage range of 44–57V, with a maximum current of 350mA. And uses two pairs of Ethernet cables for power delivery.
Applications: IP phones, basic wireless access points, and static IP cameras.
IEEE 802.3at (PoE+) — Second-Generation Standard
Released in 2009, with a maximum power output of 30W and 25.5W available to the powered device. It has a voltage range of 50–57V, a maximum current of 600mA, and uses two pairs of twisted-pair cable for power delivery.
Applications: PTZ cameras, Wi-Fi 5/Wi-Fi 6 access points, and high-definition video conferencing systems.
IEEE 802.3bt (PoE++) — Third-Generation Standard
Released in 2018, IEEE 802.3bt (PoE++) divided into Type 3 (60W/51W) and Type 4 (100W/71W). These standards use all four pairs of the Ethernet cable for power delivery (4P PoE).
Applications: Digital signage, high-power LED lighting, video conferencing systems, laptops, and 5G small cells.
Next is PoE standard compatibility: backward compatibility and potential risks
Backward Compatibility—High-Power Switches Can Power Low-Power Devices
PoE+ switches can power PoE devices, and PoE++ switches are also compatible with PoE and PoE+ devices. The power supply equipment (PSE) and the powered device (PD) automatically negotiate the power level via a protocol.
⚠️ Backward Incompatibility—Low-Power Switches Cannot Power High-Power Devices
Connecting a PTZ camera that requires 30W to a 15.4W PoE switch. Will result in the device failing to start or restarting frequently. This is the most common failure scenario in real-world installations.
⚠️ Passive PoE Pitfalls
n-standard PoE lacks a negotiation mechanism and directly outputs a fixed voltage. Connecting standard PoE devices to a passive PoE injector can damage them. Enterprises should avoid non-standard products when selecting equipment.
A “Gentle” Reminder About High-Power Ports
Always verify device specifications before deployment—older devices may be sensitive to voltage ranges.
Next are reference values for the power consumption of common enterprise devices
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Standard IP cameras
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4–8 W
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PTZ cameras
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15–25 W
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VoIP phones
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3–7 W
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Wi-Fi 5 AP
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10–15 W
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Wi-Fi 6 AP
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15–22 W
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Video conferencing system terminals
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25–45 W
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Next is the four-step selection method: From Requirements to Decision
Step 1—List all powered devices and their maximum power consumption
Check the device manuals or the nameplates on the back of each device, and record the rated power for each device.
Step 2—Calculate the total power requirement
Total requirement = Σ(maximum power consumption per device) × 1.2 (redundancy factor), while also accounting for line loss.
Step 3—Determine the Required Standard
Single device < 12.95W → PoE (802.3af) is sufficient
Single device 12.95W–25.5W → PoE+ (802.3at)
Per device 25.5W–71W → PoE++ (802.3bt)
If high-power devices may be added in the future → Select PoE++ directly; it is backward compatible
Step 4—Selecting a Switch or Injector
Number of devices ≤ 3 and an existing non-PoE switch is available → Use an injector. Number of devices ≥ 4 or setting up a new network → Use a PoE switch.
Next, as a product supplier: Recommended PoE Standards by Business Scenario
Small Offices/Retail Stores (≤10 devices)
Devices primarily consist of IP phones, basic access points, and fixed cameras → PoE (802.3af) or PoE+ (802.3at) is sufficient. An 8-port PoE+ switch offers the best value for money.
Medium-sized Enterprises/Campus Networks (10–50 devices)
Business Scenario includes Wi-Fi 6 APs, PTZ cameras, and video conferencing systems. Using PoE+ as the primary standard, with PoE++ as an option for some high-power ports. We recommend hybrid switches with some ports that support PoE++.
Large Enterprises/Smart Buildings/Industrial Settings
Includes digital signage, high-power LED lighting, interactive displays, 5G micro-base stations, etc. Using PoE++ Type 3 or Type 4. Pay attention to the switch’s total PoE budget (e.g., 600W or higher).
Outdoor/Harsh Industrial Environments
In addition to the PoE standard, there are many other factors to consider. For example: industrial-grade features such as a wide operating temperature range, DIN rail mounting, and redundant power supplies.
Most Noteworthy: The 6 Most Common Mistakes in PoE Selection
Calculating only the rated power and ignoring power surges—power consumption may double during startup
Confusing “PSE power” and “PD power”—a switch rated at 15.4W may actually only provide 12.95W to the device
Ignoring line loss—Cat5e cables up to 100 meters experience approximately 10%–15% power loss
Purchasing non-standard passive PoE devices—lacking a negotiation mechanism, which may damage equipment
Using substandard network cables—PoE+ and PoE++ require Cat5e or higher
Ignoring heat dissipation—high-power PoE switches generate significant heat in enclosed cabinets; adequate ventilation must be ensured
Last but not least: Common Questions About PoE Selection (Q&A)
Q: Can a PoE+ switch power Power over Ethernet devices?
A: Yes. PoE+ is backward compatible with 802.3af.
Q: What is the maximum transmission distance for PoE?
A: Power over Ethernet standard specifies 100 meters. High-quality network cables can still function normally at distances of around 150 meters.
Q: Does Power over Ethernet affect network speed?
A: No. PoE uses the common-mode voltage in the network cable to transmit power. Which does not affect the data transmission of differential signals.
