What Is Power Over Ethernet (PoE) And IEEE 802.3 Standards?

What Is Power Over Ethernet (PoE) And IEEE 802.3 Standards?

Published by Brexons Direct on 4th Oct 2021

Power over Ethernet integrates power and data over the same standard twisted-pair ethernet cable. Using the one cable for power and data allows transmission of both to remote devices, such as Voice over IP (VoIP) phones, Wireless Access Points (WAPs) and Internet Protocol (IP) cameras, without the need to supply separate power supplies at the equipment.

There are several methods for transmitting power over Ethernet cabling. The ones currently, as of 2021, approved by the Institute of Electrical and Electronics Engineers (IEEE) comply with: IEEE 802.3af-2003, 802.3at-2009, 802.3bt-2018

IEEE 802.3af and IEEE 802.3at PoE Standard

IEEE 802.3af-2003 (also known as Type 1) was the original PoE standard allowing up to 15.4 Watts of DC power on each port, sufficient for lower-powered VoIP phones, WAPs and static cameras. The IEEE 802.3at-2009 PoE+ standard (also known as Type 2) allows for up to 30W of power for high demand devices such as Video VoIP phones and controllable Pan Tilt & Zoom (PTZ) security cameras. 10BASE-T and 100BASE-TX protocols use two of the four pairs of an ethernet cable for data, which utilises pins 1 & 2 and 3 & 6. The power can run on pins 4 & 5 for the positive and 7 & 8 for the negative, obviating the need for a separate power supply at the device. However, all four pairs for Gigabit and higher speed data transmission are needed, so a new standard was developed.

IEEE 802.3bt PoE Standard

To meet the demand for Gigabit and higher speeds and higher power, a new PoE standard, IEEE802.3bt, was released in 2018. IEEE 802.3bt supports PoE sharing the data over all four pairs of wires, rather than separately as with the previous standard. The method of achieving this is similar to the phantom power that powers condenser microphones. Power is transmitted on the data conductors by applying a common voltage to each pair. As all twisted-pair Ethernet specifies differential data transmission over each pair with transformer coupling, there is no conflict with data transmission.

The two options within the standard are Type 3 and Type 4. Type 3 (also known as 4PPoE) allows up to 60 Watts of power per port, so it is ideal for video conferencing, multi-radio WAPs, PTZ Cameras, access control, LED lighting and building management systems (BMS). Type 4 (or High-Power PoE) provides for potentially up to 100 Watts of power. The increase in power available allows PoE use for a wide range of applications such as Laptops, Desktop Computers, Monitors, Digital Signages, and higher power LED lighting schemes. As well as Gigabit IEEE 802.3bt includes support for 2.5GBASE-T, 5GBASE-T and 10GBASE-T.

TypeIEEE StandardPower to DeviceMaximum PowerPowered PairsTypical Devices
PoEIEEE 802.3af (Type 1)12.95 W 15.4 W 2-pair, pins 4&5 for +ve pins 7&8 for -veVoIP phones, WAPs, Clocks, Non- PTZ surveillance cameras
PoE+IEEE 802.3at (Type 2)25.5 W 30 W 2-pair, pins 4&5 for +ve, pins 7&8 for -veVideo VoIP phones, PTZ cameras, EPOS, Access control and low power alarms
4PPoEIEEE 802.3bt (Type 3)
51 W
60 W All 4-pairsVideo conferencing equipment, IPTV, multi-radio WAPs, LED Lighting, Building Management Systems
4PPoEIEEE 802.3bt (Type 4)71.3 W 100 W All 4-pairsLaptops, Desktops, Monitors, Digital Signage, POS Kiosks and high power LED lighting

Cabling Infrastructure For PoE Implementation

Before delivering PoE, whether on an existing cabling infrastructure or a new installation, it is essential to consider the capability of the cable and connectivity expected to support the implementation currently and in the future.
For this section, Siemon cable and connectivity is referenced. The Siemon Company are recognised Global leaders at the forefront in setting the standards for data infrastructure and innovative cabling technology. However, whatever cabling system is decided upon, it is recommended to ensure that the chosen system is picked from a respectable manufacturer who is careful to meet and exceed the standards mentioned here.

Cable Considerations

Although Cat5e cable will support Type 1 PoE, it is advisable to consider installing Cat6 cable at the minimum to support most instances fully. Whatever the choice is UNDER NO CIRCUMSTANCES, use Copper Clad Aluminium (CCA) cable. Not only is that cable non-compliant to any of the TIA or ISO category specifications, but it is also considered dangerous as it could cause severe damage or even fires.

Remote powering of devices will give rise to temperature increase within cables, particularly with bundled cable configurations; this will be more apparent in higher power Type 3 and Type 4 PoE applications. Temperature rise may increase insertion loss at the connection and cause premature ageing of the jacket materials causing loss of transmission performance. The TIA and ISO recognise temperature levels within the standards and specify a length de-rating factor at temperatures over 20°C. In addition, for powering applications more than 60 Watts, the number of cables within a bundle is restricted and dependent on the AWG size and temperature rating of the cable. Reducing the link length and bundle size to meet these requirements can impact infrastructure design flexibility. See maximum recommended bundle sizes for details.

Connectivity Considerations

RJ-45 Plug and sockets should be plated with gold or palladium, however, disconnecting an RJ45 plug whilst PoE is active produces an arc that will erode the plating on the jack/socket contact surfaces at the arcing point. Suppose the plug/socket is not designed to take this into account ( and many do not!) or have very thin plating (which many do!). In that case, this erosion will appear at the fully mated position on the RJ-45 connectors, resulting in oxidation and high resistance contact, giving an unreliable connection that will cause much-increased bit errors, degraded network performance and possible burn-out and fire within the link.

Some connecting hardware manufacturers have ensured that arcing on the contacts is separate from the mated position. However, their contact geometry does not necessarily entirely ensure that contact erosion is entirely away from the fully mated position.

Siemon's Z-MAX®, MAX® and TERA® jacks with PowerGUARD technology benefit from a patented “crowned” contact shape which ensures arcing damage to both contacts are away from the mated position, this allows plugging and unplugging live connections without any possibility of arcing damage to either the plug or socket. See here for a detailed description.