Power over Ethernet (PoE) offers convenience, flexibility, and enhanced management capabilities by enabling power to be delivered over the same CAT5 cabling as data. This technology is especially useful for powering IP telephones, wireless LAN access points, cameras with pan tilt and zoom (PTZ), remote Ethernet switches, embedded computers, thin clients and LCDs.
The original IEEE 802.3af-2003 PoE standard provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA) supplied to each device. The IEEE standard for PoE requires Category 5 cable or higher (can operate with category 3 cable for low power levels).
The updated IEEE 802.3at-2009 PoE standard also known as PoE+ or PoE plus, provides up to 25.5 W of power.
Although 2009 standard prohibits a powered device from using all four pairs for power, some vendors have announced products that claim to be compatible with the 802.3at standard and offer up to 51 W of power over a single cable by utilizing all four pairs in the Category 5 cable. The trend for power demands seem to be up.
Compliance to Power-over-Ethernet safety standards is critical when moving beyond 60W (EE Times)and Compliance with POE safety standards is critical when moving beyond 60W (EDN) articles tells that the current generation of standards-based technology enables up to 60 watts of power to be delivered over four pairs of cabling, which also improves efficiency when compared to earlier two-pair solutions. Compliance with POE safety standards is critical when moving beyond 60W.
As the industry moves toward delivering even more power over the CAT5-or-better cabling infrastructure, system designers and network administrators alike, need to understand various emerging technology options. Some new options can bring expensive and cumbersome deployment complications and, potentially, safety risks.
Some manufacturers have touted their own 100W-per-port solutions or even 200W/port solutions that are not safe. The use of a standard Ethernet-cabling infrastructure for a single port delivering greater than 100W is simply not safe under the NEC standard. The only safe approach for powering devices over Ethernet cabling is to follow IEEE802.3at-2009 specifications. Moving beyond the LPS requirement (sub-100W/port LPS requirement of IEC 60950-1:2011) to greater-than-100W/port implementations requires that the cables be protected with special flame-resistant conduit. A metal enclosure is required if the total PD load is greater than 100W for information data equipment, or greater than 15W for TV and audio equipment.
One standardized 100W solution is one used by HDBaseT Alliance. HDBaseT Alliance is develops 100W power specifications for products that transport uncompressed, high-bandwidth multimedia content, 100BaseT Ethernet, power, and various control signals through a single LAN cable. The key differences between the HDBaseT-powering approach and those from other independent manufacturers pursuing higher power levels are that it:
- Complies with the section 33.7.1 of the IEEE802.3at-2009 standard, which mandates that all PSEs conform to International Electrotechnical Commission (IEC) 60950-1:2001 specifications including classification as a Limited Power Source (LPS) carrying no more than 100 volt-ampere (VA) – or 100W – per port without the need for special over-current protection devices, and
- Performs Powered Device (PD) detection followed by PD classification to determine a PD’s consumed power level prior to its ignition.
In a typical HDBaseT implementation, the PSE is installed and powered by a 50 to 57-volt DC power supply, and all PDs receive power directly over the HDBaseT link across all four pairs of CAT5-or-better cables. Additionally, core PoE technology has been enhanced for HDBaseT to use a 1 amp current for every two cabling pairs, 3-event classification to identify compliant PSEs, and identify the cable length/resistance (draw more power when required not exceeding 100W, rather than assuming a worst-case cabling infrastructure at all times). This enables HDBaseT technology to transfer of up to 100W of continuous DC power, per port, from one side of the HDBaseT link to the other.
HDBaseT’s ability to deliver up to 100W of power (over 100m, via a single LAN cable, without any additional power source) is actually very nicely aligned with trends in energy usage and demand. The power level is more than adequate for supporting today’s typical 40-inch LED TV, which requires 70W of power. It is expected that both LCD and LED TV monitors will soon be averaging approximately one watt of power consumption per inch of screen size. Regardless of screen size EnergyStar™ 6.0 is targeting a cap of 85 W for all screen sizes.
PoE continues to evolve and offer an even wider variety of high-value power-delivery and management capabilities.
265 Comments
Tomi Engdahl says:
https://hackaday.com/2023/08/14/adding-power-over-ethernet-support-to-a-mac-mini/
Tomi Engdahl says:
https://www.commscope.com/insights/the-enterprise-source/power-over-ethernet-and-your-networks-future/
Tomi Engdahl says:
Non standard power always on power injectors:
It just applies POE power to the blue and brown pairs, what’s the problem? Other than that it won’t work for gigabit…I guess they could’ve added a PTC as protection against a short…
If you accidentially plug in Ethernet device that is not designed for PoE in mind, you can end up flying the termination resistors on those wire pairs used for power (depends on the design if this happens or not). Could end up releasing some smoke from plugged in device, and after that might or might not work. The current surge when device is plugged in while power supply is on might not be always nice to RJ-45 connectors.
Safety (no 48V on not used outlet, no danger if fried device) and saving the connectors is reason why IEEE standard calls for device identification protocol before turning on power.
Tomi Engdahl says:
You can hope that “there should be NO connection across those pairs in a device that can’t use POE”
But the truth is that there are many devices where those wire pairs have termination resistor networks that connect them together. This practice has been quite common.
One example from
https://electronics.stackexchange.com/questions/244559/different-recommendations-for-ethernet-front-end-terminaton
It’s very common practice to connect the center taps of the line side windings to termination resistors to a common node, then through a single high-voltage cap to ground. Doesn’t mean it’s good practice, but it does save on three relatively expensive caps. This means that on those devices there’s 2R between any two pairs, where R is often 75 ohms. Apply 56V and you’ll dissipate 10W per, at least until the resistors decide they’re not rated for that.
Tomi Engdahl says:
Understanding a PoE Interface from an EMC Perspective
https://kk.htcm.de/press-releases/wuerth/wth1pi1295_en/
Waldenburg (Germany), November 14, 2023 – Würth Elektronik has published another Application Note on a special challenge in EMC. App Note ANP122 “Understanding a PoE Interface from an EMC Perspective” clarifies which electromagnetic interference must be taken into account for an Ethernet interface also used as a power supply. The application example is the RD022 reference design, in which Würth Elektronik has developed an industrial GB Ethernet USB adapter with integrated PoE functionality.
Devices with low power consumption (below 100W) networked via Ethernet can be supplied via ‘Power-over-Ethernet’ (PoE). Data transmission and power supply are realized with a network cable. With the RD022 reference design, Würth Elektronik presents a GB Ethernet USB adapter with integrated PoE functionality up to 25W. App Note ANP122, which is now available, takes an in-depth look at its electromagnetic behavior and provides design tips.
https://www.we-online.com/en/support/knowledge/application-notes?d=anp122-gigabit-poe-interface
https://www.we-online.com/en/support/knowledge/application-notes?d=rd022-gb-poe-ethernet-usb-adapter
Tomi Engdahl says:
Olimex’s New ESP32-POE2 Board Packs 25W of Power over Ethernet for Higher Current Projects
Offering 12V at 2A, 5V at 5A, or 3.3V at 1A, the ESP32-POE2 board aims at higher power projects like door lock solenoids.
https://www.hackster.io/news/olimex-s-new-esp32-poe2-board-packs-25w-of-power-over-ethernet-for-higher-current-projects-971ef369d23c
Tomi Engdahl says:
https://www.techradar.com/pro/forget-your-power-plug-this-tiny-stick-pc-can-run-from-an-unexpected-power-source-a-standard-ethernet-cable-connected-to-a-poe-switch
Tomi Engdahl says:
https://www.microchip.com/en-us/about/media-center/blog/2024/power-efficient-poe-pse-chipset-improved-surge-protection
Tomi Engdahl says:
Kuinka paljon jännitettä ja virtaa verkkokaapeli kestää?
https://fi.kbs-connector.com/info/how-much-voltage-and-current-can-the-network-65409910.html
Verkkokaapelin suurin jännitearvo 15 V on jännitearvo, joka ei aiheuta suoraa kuolemaa tai toimintakyvyttömyyttä. Normaalissa ympäristössä “turvallinen extramatala jännite”, johon ihmiskeho sallii jatkuvan kosketuksen, on 36 V. Ihmiskeho ei pysty havaitsemaan alle 36 V:n jännitettä. Ja Ethernet-dataa lähettävän ja vastaanottavan signaalin AC-korkeataajuisen signaalin jännite 100M sisällä ei ylitä 3V.
Yleensä tietokoneiden välisen verkkokaapelin siirtosignaalin AC-korkeataajuisen signaalin jännitearvo ei ylitä 3 V
Jos kuormitusta tarvitaan, sinun on käytettävä POE-laitetta, jonka jännitearvo on noin 48 V.
Tomi Engdahl says:
Waveshare Shrinks Its Raspberry Pi 5 Power-over-Ethernet HAT, Boasts Official Case Compatibility
A new, more compact L-shaped board leaves room for an official Raspberry Pi 5 Case cooling fan to do its thing.
https://www.hackster.io/news/waveshare-shrinks-its-raspberry-pi-5-power-over-ethernet-hat-boasts-official-case-compatibility-f098a82d4ed5
Tomi Engdahl says:
https://ui.com/switching/professional-max
Tomi Engdahl says:
https://www.hackster.io/alan43/a-really-small-poe-ip-camera-fc37a5
Tomi Engdahl says:
around 1.5 amperes
The maximum current rating for an RJ45 connector is typically around 1.5 amperes. This is the maximum amount of current that the connector can safely handle without overheating or becoming damaged.
https://www.a1securitycameras.com/blog/what-is-an-rj45-connector/
Tomi Engdahl says:
https://wiki.opensourceecology.org/wiki/Cat_5_Ampacity
Ethernet cable is a common type of cable – it is CAT 5 or 6 cable. It typically comes in 4 pairs, but is also available in 12 or more.
http://www.sumidacrossing.org/LayoutElectricity/MRRWire/WireAmpacity/ – says AWG 24 carries 3.5A open and 2A enclosed.
Tomi Engdahl says:
RJ12, RJ45, RJ50: max current per pin?
EEVblog
13 Dec 2020 — I push up to 1A through a wire pair ( 24Vdc and GND return) of CAT-5 and RJ45 connectors. For “Power Over Ethernet” which is an offical standard …
https://www.eevblog.com/forum/projects/rj12-rj45-rj50-max-current-per-pin/
Do not forget that the connector contacts are not the weakest point, there is also a thin wire and not very strong connection of the knives with the wire in the connector. Wurt Electric offers two types of PoE connectors: 350mA (pn 74982104400) and 600mA (pn 74984104400) both THR. Note that this is the current for a pair of contacts.