What is PoE? (Power over Ethernet)

The Power-over-Ethernet (PoE) standard enables the provision of power to network-compatible devices through the Ethernet or LAN cable. The network cable not only carries data but also supplies power. This eliminates the need for a separate power cable and reduces the installation effort required for network devices.

PoE-capable devices are typically categorized as power-sourcing equipment (PSE) and end devices, also known as powered devices (PD). PSE devices transmit or inject power into the LAN cable, while end devices or PD devices utilize the provided power. In essence, PoE can be integrated into a network using two methods: end-span PoE (e.g., switch) and mid-span PoE.

What are the advantages of PoE?

• Cost savings
  Only one cable is required for both power and data transmission, eliminating cable clutter and saving space.
  
  
• Rapid scalability
  Installing new power lines in buildings is often costly and inconvenient. With PoE, networks can be easily and cost-effectively installed or expanded.
  
  
• Versatility for various locations
  Certain areas, such as false ceilings, may not be suitable for laying power lines. PoE enables devices to be conveniently mounted in challenging locations.
  
  
• Enhanced tidiness
  By reducing the number of cables and sockets needed, PoE promotes a cleaner and more organized environment in crowded equipment rooms or distribution cabinets.
  
  
• Improved security
  PoE automatically interrupts power flow in the event of a service interruption, ensuring enhanced security.

What standards are available for PoE?

There are various standards for Power over Ethernet, each allowing different maximum power levels.

• IEEE 802.3af-2003 standard
  The PoE standard provides devices with up to 15.4 W of power on each port. Due to power loss during transmission, approximately 12.95 W effectively remain.
  
  
• IEEE 802.3at-2009 standard (PoE+)
  The newer PoE+ standard supplies devices with up to 25.5 W of power. Compared to 802.3af, nearly twice as much power is delivered through a single network cable.
  
  
• IEEE 802.3bu (PoDL)
  The PoDL standard is primarily used in industrial settings, such as vehicles or production machines, utilizing single-pair cables. It offers 10 levels of power ranging from 5 to 50 W.
  
  
• IEEE 802.3bt standard (4PPoE or PoE++)
  The latest advancement aims to provide even higher power capabilities, offering up to 55 W (level 3) and 100 W (level 4) for power supply. This means that an entire workstation, including a computer, monitor, and telephone, could be powered through the LAN cable.

Which power classes are offered for PoE (PoE classes)?

Devices that receive power through Power over Ethernet are assigned to specific PoE classes. Currently, there are standardized performance classes for Power over Ethernet, ranging from 0 to 8. Through defined procedures (handshake procedure), the end device communicates its class to the power source, known as Power Sourcing Equipment (PSE). This allows the PSE to deliver the appropriate amount of power based on the device's class. 

Grade	Standard	Max. feed power (PSE)	Max. power output (PD)
0	IEEE 802.3af	15,4 W	0,44 - 12,96 W
1		4,0 W	0,44 - 3,84 W
2		7,0 W	3,84 - 6,49 W
3		15,4 W	6,49 - 12,95 W
4	IEEE 802.3at	25,5 W	12,95 - 25,50 W
5	IEEE 802.3bt	45 W	40 W
6		60 W	51 W
7		75 W	62 W
8		90 W	71 W

Applications of PoE

PoE finds versatile applications in various settings, including homes, offices, and industrial environments. In residential settings, the technology is commonly employed to power hard-to-reach devices like webcams, surveillance cameras/IP cameras, and WLAN access points (WAP). Furthermore, PoE technology can be utilized for VoIP telephones, network routers, network switches, security card readers, time recording/access control systems, and intercom systems. In the future, the technology holds great potential for smart homes or smart offices, facilitating intelligent control of lighting and LED switches.

Furthermore, it is now feasible to power tablets through PoE using a recessed power supply unit. This allows tablets, functioning as wall-mounted Smart Home controls, to receive power and data connection simultaneously via Ethernet for distances of up to 100m. The TecLines TNT003 PoE to USB-C power supply unit enables this capability, delivering up to 95 Mbps data connection with just one cable. The recessed POE power supply with a USB C connection is particularly suitable for charging tablets securely mounted on walls (tablet holders) and complies with IEEE 802.3af/at standards.

The PoE In the industrial environment, the technology is used for sensors, meters or controllers, for example.. 

What should considered when using Power over Ethernet?

Increased attention should be given to the generation of heat and its impact on data transmission when higher currents flow through a LAN cable. The additional heat generated due to resistance can potentially affect the cable's performance. It is important to assess how the cable's heat can dissipate and adjust the maximum transmission capacity based on temperature conditions. Standards provide guidance on the expected temperature increases. For instance, when utilizing PoE with a typical Unshielded Twisted Pair (UTP) cable, the temperature rise of the cable can be up to five times. However, if a shielded cable is used, the factor reduces to approximately three.

Another consideration is the voltage drop experienced with longer LAN cables. As the cable length increases, there is a decrease in voltage, resulting in less power reaching the endpoint. Consequently, cables with larger cross-sections are required for longer distances. Ethernet cables are categorized into AWG classes (American Wire Gauge) with different conductor cross-sections. For instance, AWG22 Cat.7A cables offer better current conduction compared to AWG24 Cat.5e cables.

AWG no.	Diameter (Ø) in mm
21	0,72
22	0,64
23	0,57
24	0,51

Cable size units according to AWG

Can the range of PoE be extended?

In case the end device or PD does not receive sufficient voltage, PoE extenders can be employed. Currently, the maximum power transmission distance without a PoE extender is 100m. However, by using a PoE extender, the range can be extended up to 200 m.

Can PoE and non-PoE devices coexist in a network?

PoE devices and non-PoE end devices can operate together within a network. However, the non-PoE devices will not receive power through the network and must be connected to an alternative power source.