Terminology » Networking Basics » 802.3af PoE vs 802.3at PoE+: Key Differences

802.3af PoE vs 802.3at PoE+: Key Differences

poe power over ethernet 802.3af 802.3at networking basics

PoE (Power Over Ethernet) allows Ethernet cables to supply power to network devices using the existing data connection. IEEE 802.3af and IEEE 802.3at are standards defining PoE’s functions and capabilities, enabling network devices to receive both data and electrical power over Ethernet cables.

PoE-capable devices can be Power Sourcing Equipment (PSE), Powered Devices (PD), or both. The device transmitting power is called the PSE, while the device receiving power is the PD.

Examples of PSEs include network switches or PoE injectors designed for use with non-PoE switches. PD examples are VoIP phones, wireless access points (APs), and IP cameras.

The IEEE standard 802.3at PoE+ is an update to IEEE 802.3af PoE. The main difference is that PoE+ PSEs can deliver approximately twice as much power over a 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 Type 1

Here are the features of the 802.3af PoE Type 1 adapter:

  • Voltage range for PSE: 44 to 57 Volts; for PD: 37 to 57 Volts
  • This standard provides DC power up to 15.4W; the actual power available to the device is about 12.95W after subtracting power dissipation in the Ethernet cable.
  • Maximum current: 350mA
  • Cable resistance: 20 Ohm (Max.) for Cat.3
  • Maximum Cable Length: 100 meters (about 328 feet)

IEEE 802.3at PoE+ Type 2

The following are the features of the 802.3at PoE+ Type 2 adapter:

  • Voltage range for PSE: 50 to 57 Volts; for PD: 42.5 to 57 Volts.
  • Referred to as PoE+, it delivers DC power of about 25.5W.
  • This standard can deliver 51W of power using a single cable, utilizing all four pairs in a Cat.5 cable.
  • Maximum current: 600mA
  • Cable resistance: 12.5 Ohm (Max.) for Cat.5
  • Maximum Cable Length: 100 meters (about 328 feet).

Difference between 802.3af and 802.3at

Both require a minimum cable type of Cat.5e with 2-pair twisted cables.

Let’s compare 802.3af vs. 802.3at with respect to various parameters such as maximum power, voltage, cabling, and power management.

Parameters802.3af PoE802.3at PoE+
PoE type designationType-1Type-2
CablingCat 3, Cat 5 (or better)Cat 5 (or better)
Maximum power per PSE port15.4 W30 W
Port voltage range44 to 57 V50 to 57 V
Maximum power to PD12.95 W25.5 W
Voltage range to PD37 to 57 V42.5 to 57 V
Power managementClass 0, 1, 2, 3Class 4
Power pinsUses all four pairs of wires (Pins 1, 2, 3, 6)Uses all four pairs of wires (Pins 1, 2, 3, 6, 4, 5, 7, 8)
Use casesIP phones, small cameras, and Wi-Fi access pointsLarger 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 requiring more power, making it a preferred choice in enterprise and industrial environments where higher-powered networked devices are commonly deployed.