PoE (Power over Ethernet) defines the method of powering devices over a twisted pair cable with simultaneous data transmission. In 2009, the standard has been updated to 802.3at; also known as PoE+ or PoE Plus. The standard does not allow to power the devices over all four pairs. With almost twice the output power, it can supply cameras with high-power IR illuminators, network printers or IP phones.
The standards using a single cable for data and power transmission include USB (Universal Serial Bus). The transmission distance and the maximum load current are significantly lower than offered by PoE 802.3at that allows to transmit data and power at a distance of at least 100 m.
For PoE 802.3at, the maximum output power of the power supply is 30 W, and the voltage is 50–57 V. The voltage on the receiving side must not exceed 42.5–57 V with the maximum power input for a single device on the receiving side of 600 mA.
Table 1. IEEE 802.3at parameters
Power supply output power
Minimum power available to the receiver
Output voltage range of the power adapter
50,0 ... 57,0 V
Voltage range available at the receiver
42,5 ... 57,0 V
Maximum twisted pair resistance
12,5 Ω (Cat. 5)
Compatible twisted pair categories
Cat. 5 and higher
Guaranteed maximum distance
Some companies, e.g. Cisco, provide the capability to source power by using all four twisted pairs, e.g. UPOE (Universal Power Over Ethernet). The maximum power of the source device (power supply) is approx. 60 W, providing up to 51 W on the receiving side.
The main PoE+ advantage is the reduced cabling costs, since one cable can be used both for data and power transmission. Low voltage guarantees safety and the minimum distance with suitable cable is at least 100 m. All PoE devices are backward compatible, easy to install and use.