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802.3af PoE vs 802.3at PoE-Difference between 802.3af,802.3at Power Over Ethernet standards

This page on IEEE 802.3af PoE vs 802.3at PoE describes difference between IEEE 802.3af and 802.3at Power Over Ethernet adapter(PoE) standards.

PoE is the short form of Power Over Ethernet. The device which uses PoE standard is known as PoE adapter and is used to provide DC power using Ethernet cable. There are two standards which defines the specifications of Power Over Ethernet devices. Refer PoE basics for more information.

Both the standards defines specifications for the Powered device(PD) as well as Power Sourcing Equipment(PSE). The same have been highlighted below. PSE is the device for example switch which delivers power on ethernet cable. PD is the device powered by the PSE which consumes energy. Examples of PDs are wireless APs, IP compliant mobile phones and cameras.

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

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 Plus 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


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