View source for Power over Ethernet

{{Short description|System for delivering power along with data over an Ethernet cable}}
{{Redirect|PoE||Poe (disambiguation)}}
{{Redirect2|PoE++|4PPoE|the point-to-point protocol over ethernet|PPPoE}}
{{distinguish|text=[[Ethernet over power]] ([[HomePlug]]), particularly IEEE standard [[IEEE 1901]]}}
{{Use American English|date=December 2024}}

[[File:ZyXEL ZyAIR G-1000 and D-Link DWL-P50 20060829 2.jpg|thumb|300px|In this configuration, an Ethernet connection includes Power over Ethernet (PoE) (gray cable looping below), and a PoE splitter provides a separate data cable (gray, looping above) and power cable (black, also looping above) for a [[wireless access point]].  The splitter is the silver and black box in the middle between the wiring junction box (left) and the access point (right).  The PoE connection eliminates the need for a nearby [[power outlet]].  In another common configuration, the access point or other connected device includes internal PoE splitting and the external splitter is not necessary.]]

'''Power over Ethernet''' ('''PoE''') describes any of several [[technical standard|standards]] or [[ad hoc]] systems that pass [[electric power]] along with data on [[twisted-pair Ethernet]] cabling. This allows a single cable to provide both a data connection and enough electricity to power networked devices such as [[wireless access point]]s (WAPs), [[IP camera]]s and [[VoIP phone]]s.

==Techniques==
There are several common techniques for transmitting power over Ethernet cabling, defined within the broader [[Institute of Electrical and Electronics Engineers (IEEE)]] [[IEEE 802.3|802.3]] standard since 2003.

The three techniques are:
*''Alternative A'', which uses the same two of the four [[Balanced line|signal pairs]] that [[10BASE-T]] and [[100BASE-TX]] use for data in typical [[Cat 5|Cat&nbsp;5]] cabling.  
*''Alternative B'', which separates the data and the power conductors for 10BASE-T/100BASE-TX, making troubleshooting easier.
*''4PPoE'', which uses all four twisted pairs in parallel, increasing the achievable power. 

''Alternative A'' transmits power on the same wires as data for common 10 and {{nowrap|100 Mbit/s}} Ethernet variants. This is similar to the [[phantom power]] technique commonly used for powering condenser microphones. Power is transmitted on the data conductors by applying a common voltage to each pair. Because twisted-pair Ethernet uses [[differential signaling]], this does not interfere with [[data transmission]]. The common-mode voltage is easily extracted using the [[center tap]] of the standard Ethernet [[pulse transformer]]. For [[gigabit Ethernet]] and faster, both alternatives ''A'' and ''B'' transmit power on wire pairs also used for data since all four pairs are used for data transmission at these speeds.

''4PPoE'' provides power using all four pairs of the connectors used for twisted-pair Ethernet. This enables higher power for applications like [[pan–tilt–zoom camera]]s (PTZ), high-performance [[wireless access point]]s (WAPs), or even charging [[laptop battery|laptop batteries]].

In addition to standardizing existing practice for common-mode data pair (''Alternative A''), spare-pair (''Alternative B''), and four-pair (''4PPoE'') transmission, the IEEE PoE standards provide for signaling between the ''power sourcing equipment'' (''PSE'') and ''powered device'' (''PD''). This signaling allows the presence of a conformant device to be detected by the power source and allows the device and source to negotiate the amount of power required or available while avoiding damage to non-compatible devices.

==Standards development==
===Two- and four-pair Ethernet===
The original PoE standard, ''IEEE 802.3af-2003'',<ref>{{citation |title=802.3af-2003 |date=June 2003}}</ref> now known as ''Type 1'', provides up to 15.4&nbsp;W of [[Direct current|DC]] power (minimum {{nowrap|44 V DC}} and 350&nbsp;mA)<ref>IEEE 802.3-2005, section 2, table 33-5, item 1</ref><ref>IEEE 802.3-2005, section 2, table 33-5, item 4</ref> on each port.<ref>IEEE 802.3-2005, section 2, table 33-5, item 14</ref> Only 12.95&nbsp;W is guaranteed to be available at the powered device as some power dissipates in the cable.<ref>IEEE 802.3-2005, section 2, clause 33.3.5.2</ref>

The first update to PoE, ''IEEE 802.3at-2009'',<ref>{{citation |title=802.3at Amendment 3: Data Terminal Equipment (DTE) Power via the Media Dependent Interface (MDI) Enhancements |date=September 11, 2009}}</ref> introduced ''Type 2'', also known as ''PoE+'' or ''PoE&nbsp;plus''. It provides up to 25.5&nbsp;W and prohibits the use of four pairs simultaneously for power.<ref name="standards.ieee.org">{{cite web |url=http://standards.ieee.org/announcements/stdbd_approves_ieee802.3at.html |title=Amendment to IEEE 802.3 Standard Enhances Power Management and Increases Available Power |publisher=IEEE |access-date=2010-06-24 |archive-date=2012-10-16 |archive-url=https://web.archive.org/web/20121016220504/http://standards.ieee.org/news/ |url-status=dead }}</ref><ref>Clause 33.3.1 stating, "PDs that simultaneously require power from both Mode A and Mode B are specifically not allowed by this standard."</ref>

Both of these standards, 802.3af and 802.3at, were later incorporated into the [[IEEE 802.3-2012]] publication.<ref "802.3-2012">
{{cite book
|author      = <!-- not stated -->
|date        = 28 December 2012
|doi         = 10.1109/IEEESTD.2022.9844436
|title       = IEEE Std 802.3-2012 (Revision to IEEE Std 802.3-2008) – IEEE Standard for Ethernet
|url         = https://ieeexplore.ieee.org/document/6419735
|website     = IEEE Xplore
|publisher   = IEEE Standards Association
|isbn = 978-1-5044-8725-2
|access-date = 7 Jan 2025
}}
</ref>

Later ''Type 3'' and ''Type 4'' were introduced in ''IEEE 802.3bt-2018'', respectively allowing up to 51&nbsp;W and up to 71.3&nbsp;W delivered power, optionally by using all four pairs for power.<ref>Clause 33.3.1 stating, "A PD may indicate the ability to accept power on both pairsets from a Clause 145 PSE using TLV variable PD 4PID."</ref> Each pair needs to handle a current of up to 600&nbsp;[[Ampere|mA]] (Type&nbsp;3) or 960&nbsp;mA (Type&nbsp;4).<ref>IEEE 802.3bt ''145.1.3 System parameters''</ref> Additionally, power capabilities are defined for [[2.5GBASE-T and 5GBASE-T|2.5GBASE-T, 5GBASE-T]] and [[10GBASE-T]].<ref>{{cite web |url=http://www.ieee802.org/3/bt/public/jan16/hstewart_02_0116_baseline.pdf |title=IEEE P802.3bt/D1.5 Draft Standard for Ethernet – Amendment: Physical Layer and Management Parameters for DTE Power via MDI over 4-Pair |date=30 November 2015 |access-date=2017-04-09 |archive-date=2017-04-10 |archive-url=https://web.archive.org/web/20170410051052/http://www.ieee802.org/3/bt/public/jan16/hstewart_02_0116_baseline.pdf |url-status=live }}</ref> This development opens the door to new applications and expands the use of applications such as high-performance [[wireless access point]]s and surveillance cameras.

IEEE 802.3bt was incorporated into 802.3 in the 2022 revision.<ref "802.3-2022">
{{cite book
|author      = <!-- not stated -->
|date        = 29 July 2022
|doi         = 10.1109/IEEESTD.2022.9844436
|title       = IEEE Std 802.3-2022 (Revision of IEEE Std 802.3-2018) – IEEE Standard for Ethernet
|url         = https://ieeexplore.ieee.org/document/9844436
|website     = IEEE Xplore
|publisher   = IEEE Standards Association
|isbn = 978-1-5044-8725-2
|access-date = 7 Jan 2025
}}
</ref>

===Single-pair Ethernet===
The ''IEEE 802.3bu-2016''<ref>{{cite web |url=http://www.ieee802.org/3/bu/index.html |title=IEEE P802.3bu 1-Pair Power over Data Lines (PoDL) Task Force |date=2017-03-17 |access-date=2017-10-30 |archive-date=2017-10-10 |archive-url=https://web.archive.org/web/20171010063853/http://www.ieee802.org/3/bu/index.html |url-status=live }}</ref> amendment introduced ''single-pair'' ''Power over Data Lines ({{visible anchor|PoDL}})'' for the single-pair Ethernet standards [[100BASE-T1]] and [[1000BASE-T1]] intended for automotive and industrial applications.<ref>{{cite web |url=https://www.eenewsautomotive.com/news/new-automotive-power-over-ethernet-standard-extends-wattage-range |title=Automotive power-over-Ethernet standard extends wattage range |date=2017-03-13 |access-date=2021-01-16 |archive-date=2021-01-22 |archive-url=https://web.archive.org/web/20210122004440/https://www.eenewsautomotive.com/news/new-automotive-power-over-ethernet-standard-extends-wattage-range |url-status=live }}</ref> On the two-pair and four-pair standards, the power voltage is applied between one conductor of each of two pairs, so that within each pair there is no differential voltage other than that representing the transmitted data. With single-pair Ethernet, power is transmitted in parallel to the data. PoDL initially defined ten power classes, ranging from 0.5 to 50&nbsp;W (at PD).

Subsequently, PoDL was added to the single-pair variants [[Classic Ethernet#10BASE-T1|10BASE-T1]],<ref name="802.3cg">IEEE 802.3cg-2019</ref> [[2.5GBASE-T and 5GBASE-T|2.5GBASE-T1, 5GBASE-T1]], and [[10 Gigabit Ethernet#10GBASE-T1|10GBASE-T1]],<ref>IEEE 802.3ch-2020</ref> and {{asof|2021|lc=y}} it includes a total of 15 power classes with additional intermediate voltage and power levels.<ref name="802.3cg" />

==Uses==
{{Gallery|title=Products using PoE|width=250
|File:IP camera Ethernet power.jpg|alt1=|An [[IP camera]] powered by Power over Ethernet
|File:1140E.jpg|alt2=|[[Avaya IP Phone 1140E]] with PoE support
|File:CableFree-FOR3-Microwave-Link-20180410.jpg|alt3=|A CableFree FOR3 microwave link installed in the UAE: a full outdoor radio featuring proprietary high power over Ethernet
|File:IP-phone with PoE.jpg|alt4=| Cisco 7906 [[VoIP phone]] with PoE

}}

Examples of devices powered by PoE include:<ref name="PoE enabled devices">{{cite web |title=Power over Ethernet |work=Commercial web page |publisher=GarrettCom |url=http://www.garrettcom.co.uk/power-over-ethernet |access-date=August 6, 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110829043155/http://www.garrettcom.co.uk/power-over-ethernet |archive-date=August 29, 2011 }}</ref>
* [[VoIP]] phones
* [[IP camera]]s, including [[Pan–tilt–zoom camera|PTZs]]
* [[Wireless access point|WAPs]]
* [[IPTV|IPTV decoders]]
* Network [[Router (computing)|routers]]
* A small [[network switch]], providing a small number of Ethernet ports from one [[uplink]] cable. Such a switch may in turn pass PoE to downstream devices (termed ''PoE pass-through'').
* [[Intercom]] and [[public address system]]s
* [[Clock|Wall clocks]], with time set using [[Network Time Protocol|Network Time Protocol (NTP)]]
* Roof-mounted radios with integrated antennas, 4G/LTE-, 802.11- or 802.16-based systems used by wireless ISPs
* Outdoor [[Point-to-point (telecommunications)|point-to-point]] microwave and millimeter-wave radios and some [[Free-space optical communication|free space optics]] units, usually using non-standard, proprietary PoE
* [[Industrial control system]] components including sensors, controllers, meters etc.
* [[Access control]] components including help points, intercoms, keyless entry, etc.
* [[Lighting control system|Lighting controllers]] and [[Light-emitting diode|light-emitting diode (LED)]] [[LED lamp|lighting fixtures]]<ref name="POE LED Lighting">{{cite web |last=Makdessian |first=Alec M. |title=The Bright New Outlook For LEDs: New Drivers, New Possibilities |url=https://www.maximintegrated.com/content/dam/files/design/technical-documents/white-papers/led-white-paper.pdf |url-status=live |archive-url=https://web.archive.org/web/20221208160026/https://www.maximintegrated.com/content/dam/files/design/technical-documents/white-papers/led-white-paper.pdf |archive-date=8 December 2022 |access-date=17 February 2024 |work=[[Maxim Integrated]] |publisher=}}</ref>
* Stage and theatrical devices, such as networked audio breakout and routing boxes
* Remote [[point of sale|point-of-sale (POS)]] kiosks
* Ethernet repeaters, or ''extenders'', which may also pass PoE through to downstream devices<ref>{{cite web |url=http://www.veracityglobal.com/products/ethernet-and-poe-devices/outreach-max.aspx |title=Ethernet Extender for POE and POE Plus equipment |access-date=2015-10-26 |archive-date=2015-09-30 |archive-url=https://web.archive.org/web/20150930060346/http://www.veracityglobal.com/products/ethernet-and-poe-devices/outreach-max.aspx |url-status=live }}</ref>
* PoE splitters that output the power in a different form (e.g. [[USB hardware#USB Power Delivery|USB Power Delivery]]), to power a remote device or charge a [[mobile phone]]

==Terminology==

===Power sourcing equipment===
802.3 refers to ''Power Sourcing Equipment'' (PSE), which provides power on the Ethernet cable. This device may be a [[network switch]], in the standard ''Endpoint PSE'' (commonly called an ''endspan device'') or a ''PoE injector'', ''Midspan PSE'' in the standard, an intermediary device between a switch that does not provide PoE (or one that cannot provide sufficient power) and a PoE-powered device.<ref>Cisco Aironet technotes on [http://www.cisco.com/en/US/docs/wireless/technology/poe/technical/reference/Power.html#wp40055 1000BASE-T Midspan PSE], {{Webarchive|url=https://web.archive.org/web/20110802220854/http://www.cisco.com/en/US/docs/wireless/technology/poe/technical/reference/Power.html#wp40055 |date=2011-08-02 }} visited 18 July 2011</ref>

===Powered device===
802.3 refers to any PoE-powered piece of equipment as a ''Powered Device'' (PD). Examples include [[wireless access point]]s, [[VoIP phone]]s, and [[IP camera]]s.

Many powered devices have an auxiliary power connector for an optional external power supply. Depending on the design, some, none, or all of the device's power can be supplied from the auxiliary port,<ref name="802.3-2008, 33.3.5 PD Power">IEEE 802.3-2008, section 2, clause 33.3.5</ref><ref name="802.3at-2009, 33.3.7 PD Power">IEEE 802.3at-2009, clause 33.3.7</ref> with the auxiliary port also sometimes providing backup power in case PoE-supplied power fails.

==Power management features and integration==
[[File:5520-24-POE.JPG|thumb|right|300px|[[Avaya ERS 5500]] switch with 48 Power over Ethernet ports]]
Advocates of PoE expect PoE to become a global long-term DC power cabling standard and replace a multiplicity of individual [[AC adapter]]s, which cannot be easily centrally managed.<ref>{{citation |title=Banish Those "Wall Warts" With Power Over Ethernet |author=Dave Dwelley |work=Electronic Design |url=http://www.electronicdesign.com/displays/banish-those-wall-warts-power-over-ethernet |date=Oct 26, 2003 |access-date=2018-07-21 |archive-date=2017-11-26 |archive-url=https://web.archive.org/web/20171126003421/http://www.electronicdesign.com/displays/banish-those-wall-warts-power-over-ethernet |url-status=live }}</ref> Critics of this approach argue that PoE is inherently less efficient than AC power due to the lower voltage, and this is made worse by the thin conductors of Ethernet. Advocates of PoE, like the [[Ethernet Alliance]], point out that quoted losses are for worst-case scenarios in terms of cable quality, length and power consumption by powered devices.<ref>{{citation |url=https://www.cablinginstall.com/articles/2017/110/power-over-ethernet-cable-losses-ethernet-alliance.html |author1=David Tremblay |author2=Lennart Yseboodt |title=Clarifying misperceptions about Power over Ethernet and cable losses |date=November 10, 2017 |access-date=2018-07-21 |work=Cabling Installation and Maintenance |archive-date=2018-07-22 |archive-url=https://web.archive.org/web/20180722011438/https://www.cablinginstall.com/articles/2017/110/power-over-ethernet-cable-losses-ethernet-alliance.html |url-status=live }}</ref> In any case, where the central PoE supply replaces several dedicated AC circuits, transformers and inverters, the power loss in cabling can be justifiable.

===Integrating EEE and PoE===
The integration of PoE with the IEEE 802.3az [[Energy-Efficient Ethernet]] (EEE) standard potentially produces additional energy savings. Pre-standard integrations of EEE and PoE (such as [[Marvell Technology Group|Marvell]]'s '''EEPoE''' outlined in a May 2011 white paper) claim to achieve a savings upwards of 3&nbsp;W per link. This saving is especially significant as higher-power devices come online.<ref name="marvell1">{{citation |url=http://www.marvell.com/switching/assets/Marvell-PoE-An-Energy-Efficient-Alternative.pdf |title=Power over Ethernet (PoE): An Energy-Efficient Alternative |date=May 2011 |author1=Roman Kleinerman |author2=Daniel Feldman |publisher=Marvell |access-date=2016-08-31 |archive-date=2016-04-16 |archive-url=https://web.archive.org/web/20160416004558/http://www.marvell.com/switching/assets/Marvell-PoE-An-Energy-Efficient-Alternative.pdf |url-status=live }}</ref>

==Standard implementation==
Standards-based Power over Ethernet is implemented following the specifications in IEEE 802.3af-2003 (which was later incorporated as Clause 33 into [[IEEE 802.3-2005]]) or the 2009 update, IEEE 802.3at. The standards require [[Category 5 cable]] or better for high power levels but allow using [[Category 3 cable]] if less power is required.<ref name="33.1.1c">IEEE 802.3at-2009, clause 33.1.1c</ref>

Power is supplied as a [[common-mode signal]] over two or more of the [[Twisted pair|differential pairs]] of wires found in the [[Ethernet]] cables and comes from a power supply within a PoE-providing networking device, such as an [[Ethernet switch]], or by a ''PoE injector'', a PoE power source that can be used in combination with a non-PoE switch.

A [[phantom power]] technique is used to allow the powered pairs to also carry data.  This permits its use not only with [[10BASE-T]] and [[100BASE-TX]], which use only two of the four pairs in the cable, but also with [[1000BASE-T]] (gigabit Ethernet), [[2.5GBASE-T and 5GBASE-T|2.5GBASE-T, 5GBASE-T]], and [[10GBASE-T]] which use all four pairs for data transmission.  This is possible because all versions of Ethernet over twisted pair cable specify [[differential signaling|differential data transmission]] over each pair with [[network isolator|transformer coupling]]; the DC supply and load connections can be made to the transformer center-taps at each end. Each pair thus operates in [[Common-mode signal|common mode]] as one side of the DC supply, so two pairs are required to complete the circuit. The polarity of the DC supply may be inverted by [[Ethernet crossover cable|crossover cables]]; the powered device must operate with either pair: the spare pairs on pins 4 and 5, and 7 and 8, or the data pairs on pins 1 and 2, and 3 and 6. Polarity is defined by the standards on spare pairs, and ambiguously implemented for data pairs, with the use of a [[diode bridge]].

{| class="wikitable"
|+Comparison of PoE parameters
|-
! Official name<br>in IEEE 802.3
! Type 1
! Type 2
! Type 3
! Type 4
|-
! Common name(s)
! PoE
! PoE+
! colspan=2 | PoE++ / 4PPoE<ref name="802.3bt_0514">{{cite web |url=http://www.ieee802.org/3/bt/public/may14/abramson_01_0514.pdf |title=Base Line Text for IEEE 802.3 BT |author1=Koussalya Balasubramanian |author2=David Abramson |date=May 2014 |access-date=2017-04-02 |archive-date=2017-04-02 |archive-url=https://web.archive.org/web/20170402082938/http://www.ieee802.org/3/bt/public/may14/abramson_01_0514.pdf |url-status=live }}</ref>
|-
! Defining IEEE document
! 802.3af
! 802.3at
! colspan=2 | 802.3bt
|-
! Power available at PD<ref group=note>Most [[switched-mode power supplies]] within the powered device will lose another 10 to 25% of the available power to heat.</ref>
| {{nowrap|12.95 W}}
| {{nowrap|25.50 W}}
| {{nowrap|51 W}}
| {{nowrap|71.3 W}}
|-
! Maximum power delivered by PSE
| {{nowrap|15.40 W}}
| {{nowrap|30.0 W}}
| {{nowrap|60 W}}
| {{nowrap|90 W}}<ref>{{citation |url=https://ethernetalliance.org/wp-content/uploads/2018/04/WP_EA_Overview8023bt_FINAL.pdf |title=Overview of 802.3bt – Power over Ethernet standard |publisher=[[Ethernet Alliance]] |access-date=2024-08-19}}</ref>
|-
! Voltage range (at PSE)
| {{nowrap|44.0–57.0 V}}<ref name="Table 33.11">IEEE 802.3at-2009 Table 33-11</ref>
| colspan=2 | {{nowrap|50.0–57.0 V}}<ref name="Table 33.11"/>
| {{nowrap|52.0–57.0 V}}
|-
! Voltage range (at PD)
| {{nowrap|37.0–57.0 V}}<ref name="Table 33.18">IEEE 802.3at-2009 Table 33-18</ref>
| colspan=2 | {{nowrap|42.5–57.0 V}}<ref name="Table 33.18"/><ref name="Table 145-1">IEEE 802.3bt Table 145-1</ref>
| {{nowrap|41.1–57.0 V}}
|-
! Maximum current ''I<sub>max</sub>''
| {{nowrap|350 mA}}<ref name="table 33-1">IEEE 802.3at-2009 Table 33-1</ref>
| colspan=2 | {{nowrap|600 mA}} per pair<ref name="table 33-1"/><ref name="Table 145-1" />
| {{nowrap|960 mA}} per pair<ref name="Table 145-1" />
|-
! Maximum cable resistance per pairset
| {{nowrap|20 Ω}}<ref name="33.1.4">IEEE 802.3at-2009 ''33.1.4 Type 1 and Type 2 system parameters''</ref> ([[Category 3 cable|Category 3]])
| colspan=3 | {{nowrap|12.5 Ω}}<ref name="33.1.4" /><ref name="Table 145-1" /> ([[Category 5 cable|Category 5]])
|-
! Power management
| Three power classes {{nowrap|(1–3)}} negotiated by signature
| Four power classes {{nowrap|(1–4)}} negotiated by signature or {{nowrap|0.1 W}} steps negotiated by LLDP
| Six power classes {{nowrap|(1–6)}} negotiated by signature or {{nowrap|0.1 W}} steps negotiated by LLDP<ref>IEEE 802.3bt ''145.3.1 PD Type definitions''</ref>
| Eight power classes {{nowrap|(1–8)}} negotiated by signature or {{nowrap|0.1 W}} steps negotiated by LLDP
|-
! Derating of cable maximum ambient operating temperature
| None
| {{convert|5|C-change}} with only two pairs active, at ''I<sub>max</sub>''
| {{convert|10|C-change}} with all of the bundled cables pairs active, at ''I<sub>max</sub>''<ref name="bt_temp">IEEE 802.3bt ''145.1.3.1 Cabling requirements''</ref>
| {{convert|10|C-change}} with temperature planning required
|-
! Supported cabling
| Category 3 and Category 5<ref name="33.1.1c"/>
| colspan=3 | Category 5<ref name="33.1.1c"/><ref group=note>More stringent cable specification allows assumption of more current-carrying capacity and lower resistance (20.0&nbsp;Ω for Category 3 versus 12.5&nbsp;Ω for Category 5).</ref>
|-
! Supported modes
| Mode A (from Endpoint PSE), Mode B (from Midspan PSE)
| Mode A, Mode B
| Mode A, Mode B, 4-pair mode
| 4-pair mode mandatory
|}

Notes:
<references group=note/>

===Powering devices===
Three modes, ''Mode A'', ''Mode B'', and ''4-pair mode'', are available. (In the standard these are discussed as two Modes, with the term ''4-pair mode'' for both simultaneously.) Mode A delivers power on [[T568A]] and [[T568B]] pairs 2 and 3{{dash}}the data pairs of [[100BASE-TX]] or 10BASE-T. Mode B delivers power on pairs 1 and 4{{dash}}the pairs not used by 100BASE-TX or 10BASE-T. 4-pair mode delivers power using all four pairs. PoE can also be used with 1000BASE-T, 2.5GBASE-T, 5GBASE-T and 10GBASE-T Ethernet, in which case there are no spare pairs and all power is delivered using the ''phantom'' technique.

Mode A has two alternative configurations (MDI and MDI-X), using the same pairs but with different polarities. In Mode A, pins 1 and 2 (pair 3 in T568A wiring, pair 2 in T568B) form one side of the 48&nbsp;V DC, and pins 3 and 6 (pair 2 in T568A, pair 3 in T568B) form the other side. These are the same two pairs used for data transmission in 10BASE-T and 100BASE-TX, allowing the provision of both power and data over only two pairs in such networks. The free polarity allows PoE to accommodate crossover cables, patch cables and [[auto MDI-X]].

In Mode B, pins 4–5 (pair 1 in both T568A and T568B) form one side of the DC supply and pins 7–8 (pair 4 in both T568A and T568B) provide the return; these are the pairs 10BASE-T and 100BASE-TX do not use. Mode B, therefore, requires that all four pairs of the connectors be wired.

The ''Power Sourcing Equipment'' (''PSE''), not the ''Powered Device'' (''PD''), decides whether Mode A or Mode B shall be used. PDs that implement only Mode A or Mode B are disallowed by the standard.<ref>IEEE 802.3 ''33.3.1 PD PI''</ref> The PSE can implement Mode A, Mode B, or both (''4-pair mode''). A PD indicates that it is standards-compliant by placing a 25&nbsp;kΩ<!-- Ω --> resistor between the powered pairs. If the PSE detects a resistance that is too high or too low (including a short circuit), no power is applied. This protects devices that do not support PoE. An optional ''power class'' feature allows the PD to indicate its power requirements by changing the ''sense resistance'' at higher voltages.

To retain power, the PD must use at least 5–10&nbsp;mA for at least 60&nbsp;ms at a time. If the PD goes more than 400&nbsp;ms without meeting this requirement, the PSE will consider the device disconnected and, for safety reasons, remove power.<ref>{{citation |first1=Jacob |last1=Herbold |first2=Dave |last2=Dwelley |date=27 October 2003 |journal=Electronic Design |volume=51 |issue=24 |page=61 |url=http://elecdesign.com/Articles/Index.cfm?ArticleID=5945&pg=3 |archive-url=https://web.archive.org/web/20050320054651/http://elecdesign.com/Articles/Index.cfm?ArticleID=5945&pg=3 |archive-date=2005-03-20 |title=Banish Those "Wall Warts" With Power Over Ethernet}}</ref>

There are two types of PSE: ''Endpoint'' and ''Midspan''. Endpoint devices (commonly PoE switches) are Ethernet networking equipment that includes the power-over-Ethernet transmission circuitry. Midspan devices are ''power injectors'' that stand between a non-PoE Ethernet switch (or one that cannot provide sufficient power) and the powered device, ''injecting'' power without affecting the data. Endpoint devices are normally used in new installations or where the switch has to be replaced for other reasons (such as moving from {{nowrap|[[10/100]] Mbit/s}} to {{nowrap|1 Gbit/s}}), which makes it convenient to add the PoE capability. Midspan PSE can be used e.g. to power a single piece of equipment added to a network that does not provide PoE.

<!-- Only change if you have read and understood the relevant specifications and datasheets! -->
{| class="wikitable"
|+Stages of powering up a PoE link
|-
! rowspan=2 | Stage
! rowspan=2 | Action
! colspan=2 | Volts specified (V)
|-
! 802.3af
! 802.3at
|-
| Detection         || PSE detects if the PD has the correct signature resistance of {{nowrap|19–26.5 kΩ}}.
| colspan="2" style="text-align:center;"| {{nowrap|2.7–10.1}}
|-
| Classification    || PSE detects resistor indicating power range ([[#Power levels available|see below]]).
| colspan="2" style="text-align:center;"| {{nowrap|14.5–20.5}}
|-
| {{nowrap|Mark 1}} || PD signals it is 802.3at-capable. PD presents a {{nowrap|0.25–4 mA}} load.
|align=center| — ||align=center| {{nowrap|7–10}}
|-
| {{nowrap|Class 2}} || PSE outputs classification voltage again to indicate 802.3at capability.
|align=center| — ||align=center| {{nowrap|14.5–20.5}}
|-
| {{nowrap|Mark 2}} || PD signals it is 802.3at-capable. PD presents a {{nowrap|0.25–4 mA}} load.
|align=center| — ||align=center| {{nowrap|7–10}}
|-
| Startup           || PSE supplies startup voltage.<ref name="802.3-2008, section 2, table 33-12">IEEE 802.3-2008, section 2, table 33-12</ref><ref name="802.3at, table 33-18">IEEE 802.3at-2009, table 33-18</ref> ||align=center| {{nowrap|> 42}} ||align=center| {{nowrap|> 42}}<!-- Page 3 -->
|-
| Normal operation || PSE supplies power to device.<ref name="802.3-2008, section 2, table 33-12"/><ref name="802.3at, table 33-18"/> ||align=center| {{nowrap|37–57}} ||align=center| {{nowrap|42.5–57}}<!-- Page 14 -->
|}
IEEE 802.3at-capable devices are also referred to as ''Type 2''. 802.3at PSE may also use [[#Configuration via Ethernet layer 2 LLDP|LLDP communication]] to signal 802.3at capability.<ref name="linear-LTC4278_ds">{{cite web |title=LTC4278 IEEE 802.3at PD with Synchronous No-Opto Flyback Controller and 12V Aux Support |url=http://cds.linear.com/docs/Datasheet/4278fa.pdf |archive-url=https://web.archive.org/web/20110713210954/http://cds.linear.com/docs/Datasheet/4278fa.pdf |archive-date=2011-07-13 |website=cds.linear.com |page=15}}</ref>
{{Anchor|Power levels available}}
{| class="wikitable"
|+Power levels available<ref name="802.3s2t33.3">IEEE 802.3-2018, section 2, table 33-9</ref><ref>IEEE 802.3bt, table 145-26</ref>
|-
! Class !! Usage !! Classification current (mA) !! Power range at PD (W) !! Max power from PSE (W) !! Class description
|-
| 0 || Default  ||  0–5 || 0.44–12.94 || 15.4 || Classification unimplemented
|-
| 1 || Optional ||  8–13 || 0.44–3.84 || 4.00 || Very Low power
|-
| 2 || Optional || 16–21 || 3.84–6.49 || 7.00 || Low power
|-
| 3 || Optional || 25–31 || 6.49–12.95 || 15.4 || Mid power
|-
| 4 || Valid for Type 2 (802.3at) devices,<br />not allowed for 802.3af devices|| 35–45 || 12.95–25.50 || 30 || High power
|-
| 5 || rowspan=2 | Valid for Type 3 (802.3bt) devices || 36–44 & 1–4|| 40 (4-pair)|| 45 ||
|-
| 6 || 36–44 & 9–12|| 51 (4-pair)|| 60 ||
|-
| 7 || rowspan=2 | Valid for Type 4 (802.3bt) devices || 36–44 & 17–20 || 62 (4-pair) || 75 ||
|-
| 8 || 36–44 & 26–30 || 71.3 (4-pair) || 90 ||
|}

Class 4 can only be used by IEEE 802.3at (Type 2) devices, requiring valid Class 2 and Mark 2 currents for the power-up stages. An 802.3af device presenting a Class 4 current is non-compliant and, instead, will be treated as a Class 0 device.<ref name="802.3, section 2, 33.3.4">IEEE 802.3-2008, section 2, clause 33.3.4</ref>{{rp|13}}

===Configuration via Ethernet LLDP===
[[Link Layer Discovery Protocol]] (LLDP) is a layer-2 Ethernet protocol for managing devices. LLDP allows an exchange of information between PSE and a PD. This information is formatted in [[type–length–value]] (TLV) format. PoE standards define TLV structures used by PSE and PDs to signal and negotiate available power.

{| class="wikitable"
|+ [[LLDP]] Power via MDI TLV ''IEEE 802.3-2015''<ref name="802.3_PoETLV">IEEE 802.3 Clause 79.3.2 ''Power Via MDI TLV''</ref>
! colspan="2" style="width:60px;"| TLV Header
! colspan="8" style="width:60px;"| TLV information string
|- style="text-align:center;"
! style="width:60px;"| Type &nbsp;<br />({{nowrap|7 bits}})
! style="width:60px;"| Length <br />({{nowrap|9 bits}})
! style="width:75px;"| IEEE 802.3 [[Organizationally Unique Identifier|OUI]] &nbsp;<br />({{nowrap|3 octets}})
! IEEE 802.3 subtype<br />({{nowrap|1 octet}})
! MDI power support<ref name="RFC3621">IETF {{IETF RFC|3621}}</ref><br />({{nowrap|1 octet}})
! PSE power pair<ref name="RFC3621" /><br />({{nowrap|1 octet}})
! Power class&nbsp;<br />({{nowrap|1 octet}})
! Type/source priority&nbsp;<br />({{nowrap|1 octet}})
! PD-requested power value&nbsp;<br />({{nowrap|2 octets}})
! PSE-allocated power value&nbsp;<br />({{nowrap|2 octets}})
|-
| style="text-align:center;" | 127
| style="text-align:center;" | 12
| style="text-align:center;" | 00-12-0F
| style="text-align:center;" | 2
| Bit 0: port class (1: PSE; 0: PD)<br />Bit 1: PSE MDI power support<br />Bit 2: PSE MDI power state<br />Bit 3: PSE pairs control ability<br />Bits 4–7: reserved
| 1: signal pair<br />2: spare pair
| 1: Class 0<br />2: Class 1<br />3: Class 2<br />4: Class 3<br />5: Class 4
| Bit 7: power type (1: Type 1; 0: Type 2)<br />Bit 6: power type (1: PD; 0: PSE)<br />Bits 5–4: power source<br />Bits 3–2: reserved<br />Bits 0–1 power priority (11: low; 10: high; 01: critical; 00: unknown)
| {{nowrap|0–25.5 W}} in {{nowrap|0.1 W}} steps
| {{nowrap|0–25.5 W}} in {{nowrap|0.1 W}} steps
|}

{| class="wikitable"
|+ Legacy LLDP Power via MDI TLV ''IEEE 802.1AB-2009''<ref>IEEE 802.1AB-2009 Annex F.3 ''Power Via MDI TLV''</ref>
! colspan="2" style="width:60px;"| TLV Header
! colspan="5" style="width:60px;"| TLV information string
|- style="text-align:center;"
! style="width:60px;"| Type &nbsp;<br />({{nowrap|7 bits}})
! style="width:60px;"| Length <br />({{nowrap|9 bits}})
! style="width:75px;"| IEEE 802.3 [[Organizationally Unique Identifier|OUI]]&nbsp;<br />({{nowrap|3 octets}})
! IEEE 802.3 subtype<br />({{nowrap|1 octet}})
! MDI power support<ref name="RFC3621">IETF {{IETF RFC|3621}}</ref><br />({{nowrap|1 octet}})
! PSE power pair<ref name="RFC3621" /><br />({{nowrap|1 octet}})
! Power class&nbsp;<br />({{nowrap|1 octet}})
|-
| style="text-align:center;" | 127
| style="text-align:center;" | 7
| style="text-align:center;" | 00-12-0F
| style="text-align:center;" | 2
| Bit 0: port class (1: PSE; 0: PD)<br />Bit 1: PSE MDI power support<br />Bit 2: PSE MDI power state<br />Bit 3: PSE pairs control ability<br />Bits 7–4: reserved
| 1: signal pair<br />2: spare pair
| 1: class 0<br />2: class 1<br />3: class 2<br />4: class 3<br />5: class 4
|}

{| class="wikitable"
|+ Legacy LLDP-[[Link Layer Discovery Protocol#Media endpoint discovery extension|MED]] Advanced Power Management<ref name="ieee802-lldp-med-prop2006">{{cite web|title=LLDP / LLDP-MED Proposal for PoE Plus (2006-09-15)|url=http://www.ieee802.org/1/files/public/docs2006/ab-congdon-lldp-med-8023at-0906.pdf|access-date=2010-01-10|archive-date=2010-09-23|archive-url=https://web.archive.org/web/20100923081119/http://www.ieee802.org/1/files/public/docs2006/ab-congdon-lldp-med-8023at-0906.pdf|url-status=live}}2010-01-10</ref>{{rp|8}}
! colspan="2" style="width:60px;"| TLV Header
! colspan="2" style="width:60px;"| [[Link Layer Discovery Protocol#Media endpoint discovery extension|MED]] Header
! colspan="4" style="width:60px;"| Extended power via [[Medium dependent interface|MDI]]
|- style="text-align:center;"
! style="width:60px;"| Type &nbsp;<br />({{nowrap|7 bits}})
! style="width:60px;"| Length <br />({{nowrap|9 bits}})
! style="width:75px;"| [[Telecommunications Industry Association|TIA]] [[Organizationally Unique Identifier|OUI]] &nbsp;<br />({{nowrap|3 octets}})
! Extended power via MDI subtype&nbsp;<br />({{nowrap|1 octet}})
! Power type&nbsp;<br />({{nowrap|2 bits}})
! Power source&nbsp;<br />({{nowrap|2 bits}})
! Power priority&nbsp;<br />({{nowrap|4 bits}})
! Power value&nbsp;<br />({{nowrap|2 octets}})
|- style="text-align:center;"
| 127
| 7
| 00-12-BB
| 4
| [[#Power sourcing equipment|PSE]] or [[#Powered device|PD]]
| Normal or [[Emergency power system|Backup conservation]]
| Critical,<br /> High,<br /> Low
| {{nowrap|0–102.3 W}} in {{nowrap|0.1 W}} steps
|}

The setup phases are as follows:
* The PSE (provider) tests the PD (consumer) physically using 802.3af phase class 3.
** The PSE provides baseline power to the PD.
* The PD signals to the PSE that it as a PoE PD, indicating its maximum power and requested power.
* The PSE signals to PD that it is PoE PSE, indicating the power allotted to the PD, at which point the PD can begin consuming up to the allotted power.

The rules for this power negotiation are:
* The PD shall never request more power than the physical 802.3af class.
* The PD shall never draw more than the maximum power advertised by the PSE.
* The PSE may deny any PD drawing more power than maximum it has allowed.
* The PSE shall not reduce power allocated to the PD that is in use.
* The PSE may ''request'' reduced power, via conservation mode.<ref name="ieee802-lldp-med-prop2006" />{{rp|10}}

==Non-standard implementations==
There are more than ten proprietary implementations.<ref>{{cite web|title=Power over Ethernet (POE) proprietary pinouts|url=https://pinoutguide.com/Net/poe_pinout.shtml#poeprop}}</ref> The more common ones are discussed below.
===Cisco===<!-- section header used in redirects -->
Some Cisco WLAN access points and [[VoIP phone]]s supported a proprietary form of PoE<ref name="pinout">{{cite web |url=http://pinoutsguide.com/Net/poe_pinout.shtml |archive-url=https://web.archive.org/web/20150401193537/http://pinoutsguide.com/Net/poe_pinout.shtml |archive-date=2015-04-01 |title=Power over Ethernet (POE) pinout}}</ref> many years before there was an IEEE standard for delivering PoE. Cisco's original PoE implementation is not software upgradeable to the IEEE 802.3af standard. Cisco's original PoE equipment is capable of delivering up to {{nowrap|10 W}} per port.  The amount of power to be delivered is negotiated between the endpoint and the Cisco switch based on a power value that was added to the Cisco proprietary [[Cisco Discovery Protocol]] (CDP).  CDP is also responsible for dynamically communicating the Voice VLAN value from the Cisco switch to the Cisco VoIP Phone.

Under Cisco's pre-standard scheme, the PSE (switch) will send a [[fast link pulse]] (FLP) on the transmit pair. The PD (device) connects the transmit line to the receive line via a [[low-pass filter]]<!--some docs says relay instead, contradiction-->. The PSE gets the FLP in return. The PSE will provide a common mode current between pairs 1 and 2, resulting in {{nowrap|48 V DC}}<ref name="ciscopress_ciscophone">{{cite web|title=Planning for Cisco IP Telephony > Network Infrastructure Analysis|url=http://www.ciscopress.com/articles/article.asp?p=385336&seqNum=2&rll=1|access-date=2010-01-12|archive-date=2011-07-08|archive-url=https://web.archive.org/web/20110708155947/http://www.ciscopress.com/articles/article.asp?p=385336&seqNum=2&rll=1|url-status=live}} 2010-01-12 ciscopress.com</ref> and {{nowrap|6.3 W}}<ref name="conticomp_CAT6500POE_ds">{{cite web|title=Power over Ethernet on the Cisco Catalyst 6500 Series Switch|url=http://www.conticomp.com/PDF/CAT6500POE_ds.pdf|url-status=dead|archive-url=https://www.webcitation.org/5u2FxkQis?url=http://www.conticomp.com/PDF/CAT6500POE_ds.pdf|archive-date=2010-11-06}} 2010-01-12 conticomp.com</ref> default of allocated power. The PD must then provide Ethernet link within {{nowrap|5 seconds}} to the auto-negotiation mode switch port. A later CDP message with a TLV tells the PSE its final power requirement. A discontinuation of link pulses shuts down power.<ref name="cisco_technote00">{{cite web|title=Understanding the Cisco IP Phone 10/100 Ethernet In-Line Power Detection Algorithm – Cisco Systems|url=http://www.cisco.com/en/US/products/hw/phones/ps379/products_tech_note09186a00801189b5.shtml|access-date=2010-01-12|archive-date=2009-02-02|archive-url=https://web.archive.org/web/20090202164951/http://cisco.com/en/US/products/hw/phones/ps379/products_tech_note09186a00801189b5.shtml|url-status=live}} 2010-01-12 cisco.com</ref><!-- In-line Power Patch Panel (IPPP) send 347 kHz if return in 50 ms, 16 transitions 50/50 ms, then poll 50 ms every 600 ms device still present -->

{{anchor|UPOE}}In 2014, Cisco created another non-standard PoE implementation called '''{{vanchor|Universal Power over Ethernet}}''' ('''UPOE'''). UPOE can use all four pairs, after negotiation, to supply up to 60&nbsp;W.<ref>{{cite web |title=Cisco Universal Power Over Ethernet – Unleash the Power of your Network White Paper |url=http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-4500-series-switches/white_paper_c11-670993.html |archive-url=https://web.archive.org/web/20171128140727/http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-4500-series-switches/white_paper_c11-670993.html |archive-date=2017-11-28 |date=2014-07-11 |publisher=Cisco Systems}}</ref>

==={{anchor|LTPoE++}}Analog Devices===
A proprietary high-power development called LTPoE++, using a single Cat 5e Ethernet cable, is capable of supplying varying levels at 38.7, 52.7, 70, and 90&nbsp;W.<ref name="www.linear.com">{{cite web |url=http://www.linear.com/products/power-over-ethernet_(poe)_interface_controllers |title=Power over Ethernet Interface Controllers |access-date=2016-07-27 |archive-date=2016-07-20 |archive-url=https://web.archive.org/web/20160720141040/http://www.linear.com/products/Power-Over-Ethernet_(PoE)_Interface_Controllers |url-status=live }}</ref>

===Microsemi===
[[PowerDsine]], acquired by [[Microsemi]] in 2007, which was then acquired by Microchip in 2018, has been selling power injectors since 1999. Using Microchip's multi-PoE PSE ICs, PoE injectors and switches can support the IEEE 802.3 PoE standards and also pre-standard configurations. Several companies such as [[Polycom]], [[3Com]], [[Lucent]] and [[Nortel]] used PowerDsine's older ''Power over LAN'' PoE implementation.<ref>{{citation |url=http://www.poweroverethernet.com/sponsors.php?sponsor_id=12 |title=PowerDsine Limited |archive-url=https://web.archive.org/web/20120728191203/http://www.poweroverethernet.com/sponsors.php?sponsor_id=12 |archive-date=2012-07-28}}</ref>

===Passive===<!-- section header used in redirects -->
In a passive PoE system, the injector does not communicate with the powered device to negotiate its voltage or wattage requirements but merely supplies power at all times. Common {{nowrap|100 Mbit/s}} passive applications use the pinout of 802.3af mode B (see {{section link||Pinouts}}){{snd}}with DC positive on pins 4 and 5 and negative on 7 and 8, and data on 1 and 2, and 3 and 6, but polarization may vary. Gigabit passive injectors use a transformer on the data pins to allow power and data to share the cable and are typically compatible with 802.3af Mode A. Passive  injectors with up to 12 ports are available.<!--presumably a reference to https://www.poetexas.com/products/gpoe-12-48v120w-->

Commodity passive PoE devices often include down regulation for adding PoE to existing systems operating at 5&nbsp;volts.<ref name="Active 5v Splitter manufacturer">{{cite web |title=5 volt power over ethernet adapters |url=http://wifiqos.com/foscam.php |archive-url=https://web.archive.org/web/20130702011332/http://wifiqos.com/foscam.php |archive-date=2013-07-02}}</ref>{{Unreliable source?|date=February 2020}}

Passive PoE power sources are commonly used with a variety of indoor and outdoor wireless radio equipment, most commonly from Motorola (now Cambium), [[Ubiquiti Networks]], [[MikroTik]] and others. Earlier versions of passive PoE 24 VDC power sources shipped with 802.11a, 802.11g and 802.11n-based radios are commonly {{nowrap|100 Mbit/s}} only.

Passive DC-to-DC injectors also exist which convert a 9&nbsp;V to 36&nbsp;V DC, or 36 V to 72 V DC power source to a stabilized 24&nbsp;V 1&nbsp;A, 48&nbsp;V 0.5&nbsp;A, or up to 48 V 2.0 A PoE feed with '+' on pins 4 & 5 and '&minus;' on pins 7 & 8. These DC-to-DC PoE injectors are used in various telecom applications.<ref name="Passive PoE injector manufacturer">{{cite web|title=Passive Power over Ethernet equipment, AC-DC and DC-DC|url=http://tyconpower.com/products/POE.htm |archive-url=https://web.archive.org/web/20100620210314/http://tyconpower.com/products/POE.htm |archive-date=2010-06-20}}</ref>

==Power capacity limits==
The [[ISO/IEC]] TR 29125 and [[Cenelec]] EN 50174-99-1 draft standards outline the cable bundle temperature rise that can be expected from the use of 4PPoE. A distinction is made between two scenarios: 
# bundles heating up from the inside to the outside, and 
# bundles heating up from the outside to match the ambient temperature. 
The second scenario largely depends on the environment and installation, whereas the first is solely influenced by the cable construction. In a standard unshielded cable, the PoE-related temperature rise increases by a factor of 5. In a shielded cable, this value drops to between 2.5 and 3, depending on the design.

==Pinouts==
{| class="wikitable" style="text-align: center;"
|+ 802.3af/at/bt pin assignments from the Power Sourcing Equipment (PSE) perspective (MDI-X)
|-
! Pins at switch
! T568A color
! T568B color
! colspan=2 | 10/100 mode B, <br />DC on spares
! colspan=2 | 10/100 mode A, <br />mixed DC & data
! colspan=2 | 1000 (1&nbsp;Gbit/s) mode B, <br />DC & bi-data
! colspan=2 | 1000 (1&nbsp;Gbit/s) mode A, <br />DC & bi-data
! colspan=2 | 1000 (1&nbsp;Gbit/s) mode A+B (4PPoE), <br />DC & bi-data{{notetag|name=type34only}}
|-
! Pin 1
| [[Image:Wire white green stripe.svg|60px]]<br /> White/green&nbsp;stripe
| [[Image:Wire white orange stripe.svg|60px]]<br /> White/orange&nbsp;stripe
| Rx + || 
| Rx + || DC +
| TxRx A + ||
| TxRx A + || DC +
| TxRx A + || DC +
|-
! Pin 2
| [[Image:Wire green.svg|60px]]<br /> Green solid
| [[Image:Wire orange.svg|60px]]<br /> Orange solid
| Rx − ||
| Rx − || DC +
| TxRx A − ||
| TxRx A − || DC +
| TxRx A − || DC +
|-
! Pin 3
| [[Image:Wire white orange stripe.svg|60px]]<br />White/orange&nbsp;stripe
| [[Image:Wire white green stripe.svg|60px]]<br /> White/green&nbsp;stripe
| Tx + ||
| Tx + || DC −
| TxRx B + ||
| TxRx B + || DC −
| TxRx B + || DC −
|-
! Pin 4
| colspan= 2 | [[Image:Wire blue.svg|60px]]<br /> Blue solid
|  || DC +
| colspan=2 rowspan=2 {{n/a|Unused}}
| TxRx C + || DC +
| TxRx C + ||
| TxRx C + || DC +
|-
! Pin 5
| colspan= 2 | [[Image:Wire white blue stripe.svg|60px]]<br /> White/blue&nbsp;stripe
| || DC +
| TxRx C − || DC +
| TxRx C − ||
| TxRx C − || DC +
|-
! Pin 6
| [[Image:Wire orange.svg|60px]]<br /> Orange solid
| [[Image:Wire green.svg|60px]]<br />Green solid
| Tx − ||
| Tx − || DC −
| TxRx B − ||
| TxRx B − || DC −
| TxRx B − || DC −
|-
! Pin 7
| colspan= 2 | [[Image:Wire white brown stripe.svg|60px]]<br /> White/brown&nbsp;stripe
| || DC −
| colspan=2 rowspan=2 {{n/a|Unused}}
| TxRx D + || DC −
| TxRx D + ||
| TxRx D + || DC −
|-
! Pin 8
| colspan= 2 | [[Image:Wire brown.svg|60px]]<br /> Brown solid
| || DC −
| TxRx D − || DC −
| TxRx D − ||
| TxRx D − || DC −
|-
| colspan="13" style="text-align: left;" | Notes: {{notefoot|refs=
{{notetag|name=type34only|Only supported by 802.3bt for devices that identify as the newly added Type 3 or Type 4.<ref>IEEE 802.3bt-2018, clause 145.2.9 stating "A PSE shall not apply 4-pair power unless the PSE [...] has identified the PD as Type 3 or Type 4."</ref>}}
}}
|}

==References==
{{Reflist}}

==External links==
* [https://ieeexplore.ieee.org/browse/standards/get-program/page/series?id=68 IEEE GET Program for free download of standards after registration]
* [http://www.ieee802.org/3/af/ ieee802.org: IEEE 802.3af Task Force]
* [http://www.ieee802.org/3/at/ ieee802.org: IEEE 802.3at Task Force]
* [http://www.ieee802.org/3/bt/ ieee802.org: IEEE 802.3bt Task Force]

{{Ethernet}}

{{DEFAULTSORT:Power Over Ethernet}}
[[Category:Ethernet]]
[[Category:Networking hardware]]
[[Category:Network appliances]]
[[Category:Electric power]]
[[Category:IEEE standards]]
[[Category:Power supplies]]