What is power over ethernet?


Power over Ethernet (PoE) technology allows a twisted-pair Ethernet cable to provide power to electrical devices, in addition to data. This is commonly found in Internet of Things (IoT) devices, such as IP security cameras, and greatly simplifies the wiring of any such setup, as it means only one cable is required for almost everything. When such equipment can be placed in inaccessible places where running any cables would be cumbersome, it is really handy, not to mention cheap.

However, this is not all that makes PoE so useful. Here’s everything you need to know about Power over Ethernet.

What is Power over Ethernet?

A power over ethernet IP camera.
Oli Niemitalo/Wikimedia

Power over Ethernet is the name given to the overarching technology that facilitates the provision of power over Ethernet network connections as well as data transmission. In fact, PoE is a combination of a device that supports PoE, a standard Ethernet cable, and a network switch with PoE support. It is also possible to use a non-PoE switch, and have a PoE injector between the switch and the PoE device, but that injector will need its own main power connection to provide power to the network.

PoE was initially envisioned for use with Voice over Internet Protocol (VoIP) phones, allowing them to be powered and connected to a network with a single cable, while allowing such devices to be remotely turned off when not in use. Simple ability to do was also provided. It has since been used to provide easy wiring for applications such as IP cameras, outdoor radios, IP TVs, network routers, intercoms and entry card scanners at access control points, remote point-of-sale kiosks, and industrial control systems, to name a few. has been extended.

However, its most common use in most people’s homes is with Wi-Fi access points. This is especially common on mesh networks, where multiple routers and nodes are required.

How does Power over Ethernet work?

All the different types of Ethernet cables are made of twisted pairs of copper wires. It is these pairs that transmit data and it is these same pairs that facilitate power transmission down the cable as well. Some of that power is received by the power source device, be it a PoE switch or a PoE injector, and the rest is distributed via Ethernet cabling to any attached PoE devices.

There are three standardized technologies for delivering power over Ethernet. They are known as Alternative A (or Mode A), Alternative B (or Mode B), and 4PPoE. For Alternative A PoE configurations, power and data are transmitted over a single wire (for 10 Mbps and 100 Mbps speeds), while Alternative B transmits power and data over separate wires. The 4PPoE standard uses all four pairs of twisted-pair wires to transmit power and data. This allows for greater power delivery and network speed.

Eero PoE Gateway is installed in a cabinet.

Which Ethernet cables support PoE?

You don’t need any special type of cabling to use PoE, but you do need to choose a high enough quality Ethernet cable to deliver power and data without interference. Although the performance and quality of Ethernet cables can vary dramatically depending on the Ethernet cable you choose, the most recent ranges of cables have minimum quality limits that ensure you’ll get a reliable PoE connection. With this in mind, Category 5, or Category 5, Ethernet cables should be considered the minimum cable category used for Power over Ethernet, versus cables used for Gigabit Ethernet with PoE or higher bandwidth connections. With the more recent generation of.

One caveat with this recommendation is that the cable must be made with 100% copper wiring. Some cheap Ethernet cables are referred to as CCA, or Copper-Clad Aluminum, and they are effectively an aluminum wire wrapped in a thin layer of copper. Since aluminum is not as good an electrical conductor as copper, it is recommended not to use CCA Ethernet cables for PoE networking regardless of the desired bandwidth.

How much power can PoE provide?

Although PoE typically provides relatively low-level power for modestly connected equipment, it can provide a lot of power to facilitate some of the more demanding PoE equipment if necessary. The base Power over Ethernet specification provides up to 15.4 watts of DC power on each port, although this is typically reduced to 12.95W on the device itself, as some power is lost with cable length – more so in longer cables.

More recent specifications can provide 25.5W, 51W, or even 71W per port, each of which places greater demands on the power sourcing equipment, whether it’s a PoE-equipped switch or a PoE injection device.

How long can PoE cables be?

Although PoE does not demand any special cabling in order to function correctly, there are some limits on cable length. Different Ethernet cables support different data rates at different lengths, but PoE is also limited to 100 meters. However, while you’re limited to 100m per Ethernet cable on a PoE network, you can expand that power-delivery mechanism by using a PoE extender. You install them on the line between the power source device and the network device, giving you the option of adding up to 100 meters of Ethernet cable to the network.

PoE extenders are not injectors, so they do not require their own power connection, but they do ensure that power is maintained throughout the network. However, they do not fully replicate the power from the original source, plus the expander requires some power to operate. This results in less power being delivered to the final endpoint device than if it were simply connected directly to the power source device over a short cable run.

With this in mind, you can technically use multiple PoE extenders over the length of a network to further extend its reach, but each extender consumes more power, saving less for the final PoE device . This is further compounded if you use an extension splitter, which funnels the Power over Ethernet connection to multiple endpoint devices.

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