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The Origin and Power Supply Standards of POE

1. The origin of POE

POE is the abbreviation of Power Over Ethernet, which refers to the technology of transmitting data signals for some IP-based terminals (such as IP phones, wireless LAN access points AP, network cameras, etc.) and providing DC power supply for such devices without any changes to the existing Ethernet Cat.5 wiring infrastructure. POE technology can ensure the safety of existing structured cabling and the normal operation of existing networks and minimize the costs.

In June, 2003, IEEE approved the 802.3AF standard, which is a new standard based on the system of POE. Related standard of direct power supply through network cable is added based on IEEE 802.3, which is an extension of the existing Ethernet standard and the first international standard on power distribution. POE 802.3AF clearly specifies the power detection and control items in the remote system. It also specifies the way that routers, switches, and hubs supply power to devices such as IP phones, security systems and wireless LAN access points through Ethernet cables.

2. Power supply standard of POE

There are two aspects that determine how many cameras a POE switch can supply power to at the same time: the power supply standard and the total power supply of the POE switch. Power supply of POE switch can be regarded as single port power supply of POE switch. There are two popular POE switches in the market, which are IEEE 802.3AF and IEEE 802.3AT. POE 802.3 AF specifies the power supply as 15.4W and POE 802.3 AT specifies the power supply as 30W. Due to different power supply standards, the power of the single port is also different. For example, if the camera power is 9W, the POE switch of 802.3 AF standard is suitable. If the camera power is 20W, you can use 802.3 AT standard POE switch. If the camera power is above 30W, the POE solutions is to use a special POE power supply module.

802.3AF standard:

Power supply voltage: 44-57V

Power supply current: 10 ~ 350 mA

Maximum power supply: 15.4W

Maximum received power: 12.95W

802.3AT standard:

Power supply voltage: 50-57V

Power supply current: 10 ~ 600 mA

Maximum power supply: 30W

Maximum received power: 25.5W

Generally, the power supply of a POE switch that supports both 802.3AF and 802.3AT power supply standards is adaptive. For example, if it is connected to a 5W device, it will provide 5W power. If it is connected to a 20W device, it will provide 20W power.

Can 802.3AF and 802.3AT standards be employed universally?

802.3AT is downward compatible with 802.3AF. In other words, if your switch supports the 802.3AT standard and its maximum power supply is 30W, it can power 7W cameras that support 802.3AF standard.

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