802.3af and 802.3at PoE Standards
The Institute of Electrical and Electronic Engineers (IEEE) is responsible for creating PoE standards.
There are currently two PoE standards available. The 802.3af standard supports 15.44 watts of power. But even though 802.3af Powered Sourcing Equipment (PSE) are able to transmit 15.44 watts of power, powered devices (PDs) can only reliably receive 12.95 watts of power due to power dissipation. In 2009, IEEE introduced the higher powered 802.3at standard, also known as PoE+. The standard supports 30 watts of power, but in similar fashion to the 802.3af standard, power dissipation causes powered devices to receive slightly lower amounts of power, specifically 25.5 watts of power.
802.3BT or PoE++
IEEE is currently overseeing yet another higher powered PoE standard. As the utility of PoE expands beyond the networking sector, higher powered PoE will be able to support nurse call systems, point of sale systems, IP turrets used by financial traders, and higher powered IP cameras such as PTZ Cameras, among many other applications. 802.3bt, also known as PoE++, the new standard is expected to be ratified in early 2017, will utilize all four twisted pairs to transmit power. The 802.3bt standard will be able to achieve 49-70 watts of power using this method. The new standard will essentially combine both Mode A and Mode B to achieve the higher voltage. Some sources even site that the standard will be able to supply up to 100 watts of DC power. This newer standard will not only allow for higher power, but will also be able to support 10 Gbps connections. Type A specifies for 60W (50 watts of power) and Type B specifies for about 100 watts of power (approximately 80 watts of power with power dissipation).