Power over Ethernet (PoE) is a technology that enables electrical power to be transmitted over standard Ethernet network cables. This allows devices such as network switches, access points, and cameras to be powered directly from the Ethernet cable without the need for a separate power source.

PoE operates by sending power along with data signals over the same twisted pair of wires in an Ethernet cable. There are several standards for PoE, with the most common being IEEE 802.3af and IEEE 802.3at. These standards define the maximum power that can be transmitted over the cable, as well as the methods for detecting and negotiating power requirements between the power source and the device.

PoE has several advantages over traditional power delivery methods, including reduced installation costs and improved flexibility in device placement. It also eliminates the need for separate power supplies and reduces the risk of power failures. PoE is widely used in networked devices, including IP phones, wireless access points, security cameras, and IoT devices.

PoE can either be delivered by a networking device such as a router or switch with a PoE out port, or by a PoE injector, such as the one above.

There are several types of PoE, each defined by a specific standard.

The most common PoE types are:
IEEE 802.3af PoE: This standard provides up to 15.4 watts of power to the device and is suitable for low-power devices such as IP phones, wireless access points, and cameras.

IEEE 802.3at PoE+: This standard provides up to 30 watts of power to the device and is suitable for higher-power devices such as pan-tilt-zoom (PTZ) cameras and video phones.

IEEE 802.3bt PoE++: This standard provides up to 60 watts or 100 watts of power to the device, depending on the implementation. This standard is suitable for high-power devices such as high-performance wireless access points, outdoor cameras, and industrial devices.

Passive PoE: This type of PoE does not use any standardized protocol for negotiation or detection of power requirements. Instead, it delivers a fixed voltage to the device, which must be compatible with the device for it to work.

4-Pair PoE: This type of PoE uses all four pairs of wires in an Ethernet cable to deliver power, instead of just two pairs used by the other types. This allows for higher power delivery and reduces the amount of heat generated in the cable. 4-Pair PoE is defined by the IEEE 802.3bt standard.