Guides: Power over Ethernet
Power-over-Ethernet or PoE defines the way that an ethernet cable can be used to send both power and data to a product. The product which uses PoE is called a ‘PD’ (Powered Device) and the product which supplies the power and data – often an ethernet switch – is called the ‘PSE’ (Power Sourcing Equipment).
PDs require differing amounts of power depending upon their design and the load they are driving.
PSEs are capable of supplying different amounts of power.
These variables are addressed by a number of IEEE standards:
- PoE is described by IEEE802.3af-2003. It allows a maximum of 15.4W to be supplied.
- PoE+ is described by IEEE802.3at-2009. It allows a maximum of 25.5W to be supplied.
- PoE++ is in development and will be described by IEEE802.3bt-2017. It allows a maximum of 90W to be supplied using all 4 pairs. There are 4 different power levels available: 38.7W, 52.7W, 70W and 90W.
The wattages described above refer to the power made available by the PSE. As there are significant losses in the cable, the amount of power available at the PD is lower.