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Understanding PoE Compatibility: Powering Devices Through Ethernet

Power over Ethernet (PoE) technology has been a game-changer for network infrastructure. PoE allows for the transmission of power and data through a single Ethernet cable, simplifying installation and reducing costs. However, not all devices are compatible with PoE, which can lead to compatibility issues that can be costly and time-consuming to resolve. Therefore, understanding what PoE compatibility means before using this technology is essential.

How Does A PoE Switch Get Power?

A PoE switch gets power from an AC power source and uses that power to provide electricity and data to connected PoE-enabled devices through Ethernet cables. The PoE switch has a built-in power supply that converts the AC power to DC power, which is then used to power the PoE devices.

The PoE switch delivers power through an Ethernet cable using Power Sourcing Equipment (PSE). The PSE sends electrical power and data signals over the Ethernet cable to the device being powered—also known as a Powered Device (PD). The PoE switch automatically detects the power requirements of the connected device and provides the appropriate power level.

There are two main types of PoE: IEEE 802.3af and IEEE 802.3at. The IEEE 802.3af standard provides up to 15.4 watts of power, while the IEEE 802.3at standard, also known as PoE+, provides up to 30 watts. PoE switches must comply with the relevant standards to provide the appropriate amount of power to the connected PDs.

How Do You Power A PoE Device?

To power a PoE device, you need to connect it to a PoE-enabled network switch or PoE injector. The PoE-enabled switch or injector delivers power and data over a single Ethernet cable to the PoE device. Here are the steps needed to power a PoE device:

  1. Determine if the device is PoE compatible:Before attempting to power a device using PoE, make sure that the device is PoE-compatible. Not all devices are PoE-compatible, and trying to power a non-PoE device with a PoE switch or injector can damage the device.
  2. Connect the PoE device to a PoE-enabled switch:If you have a PoE-enabled switch, connect the PoE device to one of the switch’s PoE ports using an Ethernet cable. The PoE switch automatically detects the device’s power requirements and provides the appropriate power level.
  3. Connect the PoE device to a PoE injector:If you don’t have a PoE-enabled switch, you can use a PoE injector to power the device. Connect the PoE injector to a power source and then connect it to the PoE device using an Ethernet cable. The PoE injector provides power to the device through the Ethernet cable.
  4. Verify that the PoE device is powered on:Once you’ve connected it to a PoE-enabled switch or injector, verify that the device is receiving power by checking its status indicators or attempting to use the device.

Does PoE Use All 8 Wires (in an Ethernet Cable)?

No, PoE does not use all eight wires in an Ethernet cable. PoE uses only two of the four pairs of wires in an Ethernet cable. Typically, the spare wires are used for power transmission. More specifically, PoE uses pins 1, 2, 3, and 6 in the Ethernet cable for data transmission, while the power is transmitted over pins 4, 5, 7, and 8. This approach allows PoE to provide power to devices while simultaneously providing data transmission, making it a convenient and efficient solution for powering devices that are difficult to reach or require mobility. However, using a properly wired Ethernet cable is essential to ensure that PoE operates correctly and safely.

How Much Power Do PoE, PoE+, and PoE++ Provide?

Three main Power over Ethernet (PoE) standards exist: PoE, PoE+, and PoE++. Each of these standards provides a different level of power. It is important to distinguish between different PoE standards as devices requiring more power only work with IEEE 802.3at switches or injectors.

  • PoE (IEEE 802.3af):PoE provides up to 15.4 watts of power per port. This power level suits VoIP phones, wireless access points, and IP cameras.
  • PoE+ (IEEE 802.3at):PoE+ provides up to 30 watts of power per port, which is almost twice as much as PoE. This power level suits devices requiring more power, such as pan-tilt-zoom (PTZ) cameras, video phones, and thin clients.
  • PoE++ (IEEE 802.3bt):PoE++ is also known as 4-pair PoE, which provides up to 60 watts of power per port. This power level suits high-power devices like high-end IP cameras, access points, and LED lighting.

It’s important to note that not all PoE-enabled devices require the maximum power level. Each device has a specific power requirement, and it’s vital to ensure that the PoE switch or injector can provide the appropriate amount of power for the connected devices. For example, a standard IP phone typically requires 7 watts of power, while a pan-tilt-zoom (PTZ) camera may require up to 60 watts. By understanding the power requirements of your devices, you can ensure that you choose the right PoE switch or injector. Additionally, using a PoE-enabled smart switch will not harm the appliance, as the switch will only provide the power the device needs.

Does PoE Lose Power Over Distance?

Yes, PoE does lose power over distance. The amount of power loss depends on various factors, including the length and quality of the Ethernet cable, the power level required by the PoE device, and the PoE standard used. As the Ethernet cable length increases, the cable’s resistance also increases, resulting in voltage drop and power loss.

PoE injectors and switches compensate for the power loss by providing a slightly higher voltage than required by the device at the source end of the cable. This compensates for the voltage drop over the cable and ensures that the device receives the correct amount of power at the other end. However, there is a limit to the amount of voltage that can be added, and the maximum distance that PoE can operate effectively depends on the specific PoE standard used.

In general, IEEE 802.3af (PoE) and IEEE 802.3at (PoE+) can operate up to 100 meters (328 feet) on a standard Ethernet cable. However, IEEE 802.3bt (PoE++) can operate up to 100 meters on a Cat 6 cable and up to 200 meters on a Cat 6a cable. It’s essential to remember that the distance PoE power/data can travel across depends on many factors, including cable quality, temperature, and other environmental conditions.

The Lowdown

Using devices from the same manufacturer is recommended, as they are more likely to be compatible. Additionally, it is crucial to ensure that your network infrastructure can handle the power requirements of your devices, especially if you plan to expand your network in the future. By understanding the power requirements of your devices and choosing the right PoE switch or injector, you can ensure that your devices work together seamlessly and efficiently.

Find out more about the benefits of PoE technology here. Visit Versa Technology for featured products, announcements, and video tutorials. Contact us if you need help with any PoE networking equipment for your network needs.


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