Common Questions About 802.3 PoE

Common Questions About 802.3 PoE

Common Questions About 802.3 PoE
Common Questions About 802.3 PoE
2024-06-07 01:38:45 - last edited 2024-06-07 01:41:34

The topic was originally posted by Clive_A in Common Questions About 802.3 PoE

This Article Applies to:


All Omada PoE switches.


Common Questions:


1. Standard PoE and Passive PoE


Standard PoE:

Standard Power over Ethernet (PoE) refers to the IEEE 802.3af, 802.3at (PoE+), and 802.3bt (PoE++) standards. These standards define how power is delivered over Ethernet cables to network devices.


Key Features:

  1. Voltage: Typically delivers 48V DC.
  2. Power Delivery:
    • IEEE 802.3af (PoE): Up to 15.4W per port.
    • IEEE 802.3at (PoE+): Up to 30W per port.
    • IEEE 802.3bt (PoE++): Up to 60W (Type 3) or 100W (Type 4) per port.
  3. Compatibility: Ensures compatibility between PoE sources (like switches) and powered devices (PDs) through a negotiation process.
  4. Safety: Includes mechanisms to detect if a device is PoE-compatible before supplying power, preventing damage to non-PoE devices.
  5. Standardization: Ensures interoperability between equipment from different manufacturers.


You may also learn about it from our FAQ:

What’s PoE


Passive PoE:

Passive PoE does not adhere to IEEE standards and delivers power without any negotiation process. It simply sends a fixed voltage over the Ethernet cable.


Key Features:

  1. Voltage: Can vary widely, commonly 24V or 48V, but other voltages are also used.
  2. Power Delivery: Depends on the voltage and current provided by the power source; not standardized.
  3. Compatibility: Lacks automatic detection; the power is supplied regardless of whether the connected device supports PoE.
  4. Safety: No built-in mechanisms to check if the device is PoE-compatible, which can risk damaging non-PoE devices if connected accidentally.
  5. Standardization: No official standard; implementations can vary between manufacturers.


About our products:

First, we do not have a Passive PoE switch. If you have a Passive PoE product and it does not support dual power supply methods, unfortunately, you are forced to use the Passive PoE injector.

Second, the compatibility of our products, CPE and certain EAP models support Passive PoE. Which means if you have a CPE product, TP-Link PoE switch cannot power it up. The Passive PoE injector is required.

Third, all our switches are PoE Mode A. See the difference in the Appendix.


Here are some guides you may refer to:

How to choose PoE switch

PoE Guide to TP-Link Access Points

Overview of Omada EAP Power Supply


2. Differences between PoE Injector and PoE Splitter


PoE injector(adapter) is a common device to supply power to the PoE device. It combines both power and data and outputs the PoE.

The PoE Injector supplies steady power and data connectivity to a powered device such as PoE IP Camera, PoE AP and PoE IP Phone through an Ethernet cable.



PoE Splitter is a way to supply devices that are located far from the power outlets. 

The PoE Splitter can be used with a PoE/PoE+ switch to deliver direct current (DC) power and data to a Non-PoE device.



There is a way to use them at the same time:


Here's a guide to pick up the correct PoE products:

How to set up a POE network by using TP-Link POE products


3. Reboot Loop or any abnormal PoE behavior caused by cable length or quality


It is very common to see unstable power or reboot loops in some PoE cases. For the troubleshooting, we usually recommend you do the following steps:

1. Swap with a different Ethernet cable.

2. Try a 3ft Ethernet cable.

3. Examine if your twisted pair and plug are correctly made. You can check out the cable order in this guide: Why my PoE powered device cannot work properly when connected to the PoE Switch?

4. Avoid bending your cable and make sure the cable is intact.


If you can get stable power after step 1, your last cable is not good enough to transmit the power.

If you can get stable power after step 2, your Ethernet cable was too long and not good enough for long-range transmission.

If the pairs are not correct, your power will not be supplied.

Bending the cable can cause a bad connection in your twisted pairs. That may cause unstable power transmission.


4. PoE compatibility


We recommend you use our PoE injector or PoE products for our products. We are not able to guarantee other brands may be compatible with our products.

If you have experience with the other vendors, please troubleshoot based on the steps above.

If the issue persists after all the trying, please consider our PoE products.




1. PoE Mode:


Standard PoE uses specific wire pairs to transmit power. IEEE 802.3af and 802.3at typically use two pairs of wires for power transmission (Mode A and Mode B), while 802.3bt can use all four pairs.


Mode A: Power and data are transmitted on the same pairs (1,2 and 3,6).




Mode B: Power is transmitted on the spare pairs (4,5 and 7,8).



2. Wiring Standards:


T568A and T568B are two common wiring standards that define different wire sequences.

Although T568A and T568B differ in color sequence, they are electrically equivalent in practical use, as long as consistency is maintained throughout the network.


Update Log:


May 23rd, 2024:

Release of this article.


Recommended Threads:


Omada Switch Naming Format

SG2005P-PD PoE Budget Display Incorrectly Under 802.3 bt PoE++

Common Questions About the Hardware Version and Firmware Update




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  • If there is anything unclear in this solution post, please feel free to comment below.
  • If you encounter such an issue, please follow the troubleshooting above to check your settings. Besides, ensure your Omada Controller and Switch are running with the latest firmware.
  • If the issue still exists after you try the suggestion above, please feel free to comment below or contact our support team with a detailed description of your issue and the steps you have tried.


Thank you in advance for your valuable feedback!



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