How to get the long distance Power over Ethernet
Power over Ethernet (PoE) offers a solution for transmitting both power and data over a single Ethernet cable, leading to reduced installation costs. However, PoE has a limitation of 100 meters, which is related to both data communication and voltage drop. According to the IEEE 802 standard, the maximum distance for network connections between two IP devices is 100 meters. The PoE system requires that the voltage at the endpoint device remains above DC 38V; otherwise, the power system will cease to function.
Typically, a PoE switch supplies 48V DC power through the Ethernet cable. After a transmission distance of 100 meters, the remaining voltage may decrease to 39V, which still meets the required specifications. However, if power is transmitted beyond 100 meters without appropriate design, power loss can become problematic. Therefore, it is essential to address both networking and power limitations to achieve longer distances for PoE.
There are three methods to extend power over Ethernet:
（1） The first one is the PoE extender. A single PoE extender can extend PoE to 200 meters, cascade three PoE extenders to reach a maximum 400 meters transmission distance.
Each PoE extender can enhance both network connectivity and power distribution. However, it is important to account for energy loss along the cable. Since only two twisted pairs are used for power transmission—similar to a 22AWG copper cable—only 7.91W of power remains available at the end of a 400-meter run. The lost power is dissipated as heat in the twisted pairs. Power loss is influenced not only by the transmission distance but also by the quality of the Ethernet cable used. For optimal performance in PoE applications, pure copper Ethernet cables are the preferred choice. According to our tests, when utilizing low-cost copper-clad aluminum cables, the maximum PoE distance may be reduced to 60 meters. In contrast, using Cat6 pure copper cables can extend this distance up to 120 meters. The Cat5e and Cat6 grades specify only the data rate and do not indicate the material of the Ethernet cable. When selecting an Ethernet cable, always ensure that the twisted pairs are made of pure copper.
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（2）The second option is a PoE switch that offers CCTV mode or VLAN support.
When the CCTV mode on the switch is activated, it can support transmission distances of up to 250 meters. However, there is a downside to using CCTV mode: the network speed will be reduced to 10 Mbps. This trade-off in network speed (data rate) is necessary for the increased distance. Since most IP cameras require less than 8 Mbps of bandwidth, this solution works well for IP surveillance cameras. However, if you need to extend the network for access points or small cells, the CCTV mode PoE switch is not the ideal choice, as 10 Mbps is insufficient bandwidth for multiple users accessing the network simultaneously. The CCTV mode will also automatically activate the VLAN. The VLAN ensures that each port has a dedicated bandwidth of 10 Mbps. Port 1 cannot draw bandwidth from Port 2. What is VLAN? The VLAN isolates the PoE ports, allowing each PoE port to communicate only with uplink ports, not with each other. Essentially, the PoE ports do not see one another within the LAN. Next, how does the CCTV mode switch address voltage drops? A CCTV mode PoE switch typically injects power at a higher voltage than DC 48V, often around DC 55V, to provide a greater margin for accommodating voltage drops that may occur after 250 meters of transmission.
（3）The third solution is the fiber power system.
Fiber optics have minimal limitations for network communication, with a typical range of 10 kilometers for most fiber networks. The primary challenge is voltage drop. However, the introduction of composite fiber cables, which integrate copper wiring, allows for both optical data and power to be transmitted through a single composite cable.
The fiber power system operates similarly to a conventional Power over Ethernet (PoE) system. Power is injected into the composite fiber cable at the center. Upon reaching the front end, the power, together with the optical fiber, interacts with a PoE fiber extender. This extender integrates power management and media conversion, allowing it to convert the incoming power into standard PoE output for conventional PoE devices, such as PoE IP cameras. The extent of voltage drop is influenced by the thickness of the copper cable, with the thickest composite copper available on the market being 12 AWG. This size helps minimize voltage drop, ensuring sufficient voltage is maintained over long distances. With proper design, the fiber power system can effectively transmit power over distances of 2500 to 3000 meters from the center while providing standard PoE output.
Other than long distances, there is also a demand for high power output in new IoT devices. The IEEE 802.3 af/at standard allows for a maximum power output of 25.5W. However, the new Power over Ethernet (PoE) standard, IEEE 802.3bt, utilizes all four twisted pairs to deliver power, enabling devices to provide a maximum output of 71W. This advancement will benefit power-intensive devices such as LED lighting, PTZ cameras, point-of-sale terminals, and thin clients. Transmitting high power over long distances will present new challenges in the coming years, as higher currents result in increased power loss. We look forward to observing how this technology evolves.