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How many devices can be powered by a PoE switch?

  • Author:Grace Liu
  • Source:www.mvteamcctv.com
  • Release on :2016-10-13
With the development of power supply technology, many network devices support PoE. In the network monitoring construction, in order to reduce wiring costs,many projects will consider using PoE switch to power for IP cameras.

PoE switch power supply standards
To see how many cameras can be powered by a PoE switch at the same time, consider two aspects: the power supply standard of the PoE switch and the total power of the PoE switch.
PoE switch power supply power can be understood as PoE switch single-port power supply. There are two kinds of popular PoE switches in the market, IEEE802.3af and IEEE802.3at.

IEEE802.3af standard defines the power supply is 15.4W per port, IEEE802.3at standard defines the power supply up to 30W per port.Due to different power supply standard,single-port power supply is also different. For example, the camera power is 9W, using the af standard PoE switch ; If the camera power is 20W, need use the at standard PoE switch; if the camera power is 30W or more, need to use a dedicated PoE module.

In general, a PoE switch which supports both the af and at standards has an adaptive power supply. For example, it is connected to a 5W device, then provide 5W power; if the connection is 20W equipment, then provide 20W power.

Total power of the PoE switch
The total power of the PoE switch is a very important indicator, directly related to how many cameras can be powered. For a 24 ports PoE switch with 400W power, the total power of the PoE switch is about 370W after reducing the loss.

Under the IEEE802.3af standard, it can be for 24 ports (370 / 15.4 = 24), mean support  power for 24 cameras at the same time---full load power supply. 
MVTEAM POE switches are IEEE802.3af standard,fit power for IP Cameras.
How many devices can be powered by a PoE switch?

But if according to IEEE802.3at standard,calculate single port 30W(max), it only can power for 12 cameras at the same time (370/30 =12).

In fact,the max power of IP camera is lower, basically no more than 15W, then if each PoE port reserve power according to the maximum power (such as 30W) ,there will be power waste for some ports, and some ports can not get power.

For example, some PoE switches support dynamic power allocation, which can avoid above problems. It's better to buy the switches which support dynamic power allocation, then each port is only assigned the actual power used.

Summary:
1. In order to maximize the efficiency of power supply,adopt the POE switches which support dynamic power allocation.
2. Know the maximum power consumption of the powered device, and then divide the PoE switch's total power supply power(eg:370W) by the maximum power consumption(eg:15.4w) to obtain how many devices can be powered by a PoE switch.


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