Understanding Power Consumption of PoE Ethernet Switch

As PoE changes to meet today’s increasing application requirements like IP cameras or WiFi access points, it’s widely used for enterprises networks. Using a PoE or PoE+ switch, technicians can simplify the cabling installation because the PoE technology can support power and data transmission over the same cables. When choosing a PoE Ethernet switch, we always care about the ports and power consumption most. This article will introduce the power consumption of PoE Ethernet switch and take two PoE Ethernet switches as examples to explain power consumption.

What Is Power Consumption of PoE Ethernet Switch?

At present, PoE power consumption follows two standards, IEEE 802.3af and 802.3at. The original IEEE 802.3af rules that power consumption on each port of a PoE network switch can be up to 15.4W. The updated IEEE 802.3at standard also named PoE+, which is backward-compatible with IEEE 802.3af, provides up to 25.5W of power on each port. However, because the power dissipate exists in cables, the minimum output power assured on each port for PoE switch is 12.95W, and 25.5W for PoE+ switch.

power consumption standard

Figure 1: IEEE 802.3af and IEEE 802.3at standards.

The key to successful PoE installation is to ensure that the selected power over Ethernet switch provides the necessary watts of PoE required for each device, and the total power consumption also must be guaranteed for powering all devices. Simply put, the total power consumption of all the connected devices must be controlled in the range of the PoE switch max power consumption.

How Many Devices Can I Connect to My PoE Ethernet Switches?

Power consumption of 150W and 400W are the most popular choices on the market. The following are two switches from FS, 8 port PoE switch and 24 port PoE switch, and we’ll use them to further explain the question how many devices can we connect to my PoE Ethernet switches.

PoE Ethernet switches applications

Figure 2: How many devices can be connected to a PoE switch?

How Many Devices Can the 8 Port PoE Switch Connect?

FS S1150-8T2F switch is a managed PoE+ switch. It has 8 10/100/1000Base-T RJ45 ports, and 2 Gigabit SFP slots. Its PoE standard complies with IEEE802.3af/at. And designed with a max power consumption of 150W, each port can support up to 30W power. This means the switch provides the availability of PoE on all 8 RJ45 ports, and each port can potentially power devices that are connected. From the above, we know the standard PoE can supply 15.4W power for each port, and 30W for PoE+. Therefore, this switch can simultaneously connect 8(15.4W×8=123.2W<150W) devices that use IEEE 802.3af standard, and only 5(30W×5=150W) devices that use IEEE 802.3at standard. For example, if a typical outdoor IP camera needs a PoE power of 20W, the connection of 7 typical IP cameras will require 140W of PoE power (7×20W), which is well within the power consumption of this network switch.

How Many Devices Can the 24 Port PoE Switch Connect?

FS S1400-24T4F managed PoE+ switch is designed with 24 Gigabit PoE+ ports, 1 console port and 4 Gigabit SFP ports. This switch complies with IEEE 802.3af/at with a max power consumption of 400W and 30W for each port. Through a calculation, we know the 24 port switch can connect 24(15.4W×24=369.6W<400W) devices with PoE standard at the same time, and support 13(30W×13=390W<400W) devices with PoE+ standard. And as for the same outdoor IP camera with a power requirement of 20W, the 24 port switch can support 20(20×20W=400W) cameras.


Knowing the power consumption of PoE Ethernet switches is very important. If you want to connect multiple devices to a PoE switch, you need to calculate the total power consumption that all the devices require, and make sure you PoE switch can provide the needed current.

Author: Feisu

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