PoE (Power over Ethernet) is a networking feature defined by the IEEE 802.3af and 802.3at standards. PoE lets Ethernet cables supply power to network devices over the existing data connection.
PoE-capable devices can be power sourcing equipment (PSE), powered devices (PDs), or sometimes both. The device that transmits power is a PSE, while the device that is powered is a PD. Most PSEs are either network switches or PoE injectors intended for use with non-PoE switches. Common examples of PDs include VoIP phones, wireless access points, and IP cameras.
PoE+, the update to PoE, is the IEEE 802.3at standard. The major difference between 802.3af (PoE) and 802.3at (PoE+) is that PoE+ PSEs can provide almost twice as much power over a single Ethernet cable. Amcrest cameras with PoE+ capabilities can only be powered by using a PoE+ PSE such as a PoE+ switch or PoE+ injector or with the included power supply.
PoE+ PSEs can supply power to both PoE and PoE+ PDs, but PoE PSEs can only supply power to PoE PDs. PoE+ PDs require more power than PoE PSEs can provide.
Note: Ethernet, PoE, and PoE+ restrict cable distances up to 100 meters (328 feet) between network ports. Anything exceeding this limit may result in signal degradation or insufficient power to the PD. In such cases, an Ethernet and PoE extender may be recommended.
What is the difference between PoE and PoE+?
- PoE is the 802.3af standard, and PoE+ is the 802.3at standard.
- The main difference between the 802.3af (PoE) and 802.3at (PoE+) standards is the maximum amount of power they provide over the Cat5 cabling.
- The maximum amount of power for the 802.3af (PoE) standard is 15.4 watts.
- The maximum for the 802.3at (PoE+) standard is 25.5 watts.
As defined in IEEE 802.3af and IEEE 802.3at, PoE delivers electrical power over two pairs out of the four twisted pairs of cable in Class D (also known as Cat5e) or better, cabling as specified in ISO/IEC 11801:1995. A PSE uses only signal pairs, the pairs 1, 2, and 3, 6, to transport power from the PSE to the PD and leaves the spare pairs, the pairs 4, 5, and 7, 8, idle. This architecture can deliver up to 30W per port.
PoE, PoE Plus/PoE+ Comparison
|Minimum cable type||Cat5e||Cat5e|
|IEEE standard definition||802.3af||802.3at|
|Maximum power per PSE port||15.4W||30W|
|Maximum power to PD||12.95W||25.5W|
|Twisted pair used||2-pair||2-pair|
How much power can PoE devices supply?
PoE+ devices can supply a maximum of 30 watts per port, while PoE devices can supply a maximum of 15.4 watts per port. However, some power is always lost over the length of the cable, and more power is lost over longer cable runs. The minimum guaranteed power available at the PD is 12.95 watts per port for PoE and 25.5 watts per port for PoE+.
PSEs also have a maximum power budget, which is the total amount of power they can supply to PDs at one time, measured in watts. Most PSEs do not have a high enough power budget to supply the maximum possible power to all PoE-capable ports, because most users do not require that much power. When you are shopping for a PoE-capable PSE, make sure that you calculate your required power budget carefully for all of the PDs you plan to connect to.
Can I mix PoE and non-PoE devices in my network?
PoE devices can be mixed in a network with non-PoE devices, but non-PoE devices cannot provide power for PDs or be powered by PSEs. The non-PoE devices must have a separate source of power.