How many cameras can the POE switch supply at the same time?

- Oct 21, 2017-

A lot of people just know POE switch, do not know how much a POE switch to monitor the camera, read the author of this article, it is not easy to pour everyone. The author engaged in OPTFOCUS POE switch sales for many years, and also sporadic several monitoring projects, the following is my experience.

To understand how many cameras the POE switch can receive at the same time, see three aspects: the POE Switch power supply standard, the POE switch total power supply, the camera's code flow. 

1, POE Switch power supply standard

There are two criteria for the popular POE switch in the market, IEEE802.3af and IEEE802.3 at, respectively define the power supply for the 15.4W and 30W, but the actual power supply power is 12. 95W and 25W due to loss during transmission.

When using a POE switch that supports the IEEE802.3AF Standard, the power of an electrical device cannot exceed that of 12.95W; when using the IEEE802.3AT Standard POE switch, the power device cannot exceed 25W.

Generally, one supports IEEE802.3af/at Standard POE switch, power supply is adaptive. For example, it is connected to a 5W device, then provides 5W of power, if the connection is 20W devices, then provide 20W power.

2, The total power supply of POE switch

This can be judged from the total power of the POE switch. Under the IEEE802.3AF Standard, if the total power of POE for a 24-port POE switch reaches 370W, it will be able to fill 24 ports (370/15.4=24), But if it is based on IEEE802.3AT Standard single-port maximum power 30W calculation, at the same time can only give 12 of the power supply (370/30=12).

For example, a 8-port Poe switch that supports IEEE802.3af/at standard, the power of a single camera is 11W, then the switch can be connected to 8 such cameras; If the power of a single camera is 20W, it's best to reserve one to two ports, and 5-6 cameras are recommended.

3, the camera's code flow

If the simple from the Poe Switch power supply is inaccurate, because the network monitoring requirements HD and smooth, so also according to the camera's code flow, after all, the Poe switch is not only power, but also the transmission of video data.

The code flow of the common camera: 720P (1 million pixel) stream is 4.5M, 960P (1.3 million pixel) stream is 6M, 1080P (2 million pixel) stream is 8M, 3 million pixel stream is 10M, 5 million pixel stream is 13-15m.

In the transmission of video data, the actual utilization of the POE switch bandwidth is only about 60%.

For example, a 8-port POE switch, the port transmission rate is hundred trillion, the camera is 720P, how many such cameras can be connected?

The 720P Camera code stream is 4.5M, the available bandwidth of this Poe switch is approximately 60Mbps, 60/4.5 is about 13, because the POE switch has only 8 Poe power ports, so it can be loaded.

By the same token, if the 8-Gigabit Poe switch is plugged into a 1080P camera, the maximum number of cameras will be 7.

In the actual use of POE switch, it is necessary to consider the power supply, but also consider the camera code flow, must be satisfied with the two, will be used safely smooth.

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