802.3af vs 802.3at PoE+

PoE (Power Over Ethernet) enables ethernet cables to supply power to networking devices over existing data connection. IEEE 802.3af and IEEE 802.3at are standards which define the functions and capabilities of PoE, enabling network devices to receive both data and electrical power over Ethernet cables.

PoE capable devices can be Power Sourcing Equipment(PSE), Powered device(PD) or both. The device which transmits power is called PSE while the device which receives power is called PD. Examples of PSEs are network switches or PoE injectors designed for use with non-PoE switches. Examples of PDs are VoIP phones, wireless access points (APs) and IP cameras. The IEEE standard 802.3at PoE+ is the update to IEEE 802.3af PoE. The major difference between 802.3af (PoE) and 802.3at (PoE+) is that, PoE+ PSEs can deliver approx. twice more power over single ethernet cable. PoE+ PSEs can supply power to both PoE and PoE+ PDs but PoE PSEs can only supply power to PoE PDs.

IEEE 802.3af PoE type1

Following are the features of 802.3af PoE type1 adapter:
• Voltage range for PSE is 44 to 57 Volt and for PD is 37 to 57 Volt
• This standard provides DC power upto 15.4 W, actual power available to the device will be about 12.95W after substracting power dissipation of the ethernet cable.
• Max. current is 350mA
• Cable resistance is 20 Ohm(Max.) for Cat.3
• Maximum Cable Length: 100 meters (about 328 feet).

IEEE 802.3at PoE+ type2

Following are the features of 802.3at PoE+ type2 adapter:
• Voltage range for PSE is 50 to 57 Volt and for PD is 42.5 to 57 Volt.
• It is referred as PoE+ and delivers DC power of about 25.5 W. This standard can deliver 51 W power using single cable utilizing all 4 pairs in a Cat.5 cable.
• Max. current is 600mA
• Cable resistance is 12.5 Ohm(Max.) for Cat.5
• Maximum Cable Length: 100 meters (about 328 feet).

Difference between 802.3af and 802.3at

Both requires minimum cable type cat.5e with 2 pair twisted pair cables. Let us compare 802.3af vs 802.3at with respect to various comparison parameters such as maximum power, Voltage, Cabling, power management etc.

Parameters 802.3af PoE 802.3at PoE+
PoE type designation Type-1 Type-2
Cabling Cat 3, Cat 5 (or better) Cat 5 (or better)
Maximum power per PSE port 15.4 W 30 W
Port voltage range 44 to 57 V 50 to 57 V
Maximum power to PD 12.95 W 25.5 W
Voltage range to PD 37 to 57 V 42.5 to 57 V
Power management Class 0, 1, 2, 3 Class 4
Power pins uses all four pairs of wires (Pins 1, 2, 3, 6) for power transmission uses all four pairs of wires (Pins 1, 2, 3, 6, 4, 5, 7, 8) for power transmission, which allows for higher power output
Use cases IP phones, small cameras, and wifi access points. larger cameras, some laptops and more power-hungry access points

Conclusion : These differences highlight the increased power delivery capabilities and broader device compatibility of IEEE 802.3at (PoE+) compared to IEEE 802.3af (PoE). PoE+ is better suited for devices that require more power, making it a preferred choice in enterprise and industrial environments where higher-powered networked devices are commonly deployed.

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