Power over Ethernet (PoE) began as an effort to save money. Engineers were looking for a way to get power and data delivered over existing copper networks that were left behind from old telephone systems found in many office buildings. PoE combines data transmission and power-supplying hardware into the same RJ45 Ethernet connector to allow for power transmission over network cabling.
Cables have advanced much more slowly than the PoE technologies they connect to, but many networks function well using legacy Cat5e and Cat6 cables. What’s different here is the ability for switches to support the greater sophistication required to send increasing amounts of data in more synchronized patterns. This allows more devices to function optimally while sharing the same network.
Let’s discuss how PoE power works and discover how more power can be transmitted from the same cables.
How Does A PoE Switch Get Power?
PoE networks source power on the network switch side (or from a power injector) to add power to an existing data line. They use a combination of these sources to send power to connected devices. The power injectors serve as a bridge between the power source and the connected devices to transmit both data and power. They inject power into a network cable to ensure that a connected device can receive power and operate without a connected DC power supply.
How Do You Power PoE Devices?
A PoE switch combines a switch and all the functionality that comes with it, with a power source. In a PoE setup, wireless access points and other devices, such as VoIP phones and IP cameras, are connected via multiple Ethernet ports. The switch provides power to these connected devices, eliminating the need for separate power cables.
Does PoE Use All 8 Wires (in An Ethernet Cable)?
An Ethernet cable has eight wires, but either a combination of four or all eight wires are used in PoE. Wires are twisted into pairs and coupled for both sides of the DC supply.
There are three main configurations for transmitting power over Ethernet cabling.
- Mode A: Also known as common-mode data pair power. Mode A combines pins 1 &2 for positive voltage (V+) and pins 3 &6 for negative voltage (V-).
- Mode B: In Mode B, the remaining spare pairs are used. The blue and white/blue wires (pins 4 and 5) are used for V+. The white/brown and brown wires (pins 7 and 8 on the RJ45 plug) are used for V-.
- 4PPoE: In 4-Pair PoE power, all four pairs of the Ethernet are used for power transmission. Combinations are pins 1&2 and pins 4&5 for positive power, and pins 3&6 and 7&8 for negative power.
Network data cables also have eight wires, but do not require all eight for a data connection. An unused pair of wires is therefore used to carry direct current (DC) voltage to the end device.
How Much Power Do PoE, PoE+, and PoE++ Provide?
Power over Ethernet technology is based on standards created by the Institute of Electrical and Electronics Engineers (IEEE). There are currently three PoE standards and switch types, each delivering a different level of power.
This standard allows a powered device to receive up to 12.95W PoE wattage using two of the four available twisted pairs of Ethernet cabling. A PoE switch supports a maximum power consumption of 15.4W per PoE port, with a voltage range between 44V and 57V.
PoE+ technology can support higher power consumption than the previous generation. It provides 30W of power to each port to ensure 25.5W at the endpoint. It also supplies power over two pairs of wires.
PoE++ technology can be classified into two types:
- Type 3 uses two or all 4 twisted pairs of wires in a copper cable to deliver up to 51W of power.
- Type 4 delivers up to 71W over 4 twisted pairs in an Ethernet cable.
PoE++ switches support up to 60W of power to each port under Type 3 and up to 100W on each PoE port under Type 4. This is the highest level of power for PoE switches.
Does PoE Lose Power over Delivery?
PoE loses minimal power over delivery. However, an 8-port PoE switch has a total PoE power budget of 130W. If used at total capacity, the maximum power yield per port would be 130W divided by eight ports, or 16.25W.
What Is The Maximum Allowable Distance between PoE Cables?
Regardless of where the power is injected, PoE can transmit 100 meters. This limitation is not because of the wires carrying power but rather, the Ethernet cabling standard’s limit on the total length of cable. Wires carrying electricity by themselves can power any device at any distance, provided enough power is generated at the source to operate the connected device on the other end of the cable run. A PoE extender can lengthen that span considerably.
What Is A PoE Extender?
A PoE extender is a plug-in device used to lengthen a network beyond the basic 100-meter distance limit. Extenders usually stretch the maximum distance of PoE cabling to about 4,100 feet from the source. That’s an increase of more than 12 times the length of a single cable alone. This plug-and-go technology can unite networks that span larger distances in settings such as shopping malls, hotels, academic and business campuses, large enterprises, and sporting venues.
What Are Some of The Major Applications for High-Power PoE?
High-power PoE is particularly useful for powering PoE lighting platforms and other smart technologies. These applications can be automated, and automation requires more power.
Applications for high-power PoE include:
- LED lighting and sensors
- High-performance WAPs
- PTZ cameras
- VoIP phones
- IP security cameras
- Thin client computers
- Digital signage
- Facility monitoring controls
- Point-of-sale kiosks
Smart device consumers are learning about what is possible with PoE and are taking steps to upgrade their supporting infrastructure.