Power over Ethernet (PoE) is a standard that provides DC electrical power along with the data over twisted-pair Ethernet cabling. There are two main modes for delivering power, referred to as Mode A and Mode B.
Mode A, also known as endspan, transmits both data and power on the orange and green wire pairs. This mode is typically used when both power and data originate from the same power sourcing equipment (PSE), like a PoE-enabled switch.
Mode B, also known as midspan, transmits power on the blue and brown pairs and data on the orange and green pairs. PoE injectors, which add power to a standard Ethernet port, often use Mode B to power devices.
The standard PoE voltage is between 44–57V, with 48V being the most common. PoE is commonly used to power devices like wireless access points, VoIP phones, and IP cameras.
Over the years, PoE has evolved with several IEEE standards that define different power levels for various applications:
- 802.3af (PoE) provides up to 15.4W of power over Cat5 or better Ethernet cables. It is suitable for devices with lower power needs, such as IP phones and basic wireless access points.
- 802.3at (PoE+) provides up to 30W of power and can support higher-power devices like advanced wireless access points and some pan-tilt-zoom cameras.
- 802.3bt (PoE++ or 4PPoE) adds more power levels, delivering up to 60W or even 90W. This is suitable for power-intensive devices like video conferencing systems, LED lighting, and high-performance wireless access points.