6 Things You Should Know About PoE Switch [FAQ]

Updated on Nov 29, 2021 by

PoE Switch


Due to the power and information transfer benefits of PoE switches, they have gained increasing attention as a popular solution for enterprises looking to provide power and data to their devices over a single connection. However, some people in the market are still confused about it. This article will address some common questions about PoE switches, such as Do PoE switches slow down speed? Can a PoE switch be connected to non-PoE devices? How to determine how much power PoE switch is needed? Here it will help you answer your questions in the process of buying or using a PoE switch.

Do PoE Switches Affect Speed?

In most businesses and homes today, fast Internet speeds are a prerequisite for productivity and profitability. Therefore, everyone is concerned that whether PoE switches will affect speed. The answer is no. The speed of your Internet will not be slowed down by an Ethernet connection, despite the fact that it is not wireless like a wifi connection. It allows speedier Internet access for connected devices as well as a more stable Ethernet connection. For data and power, PoE switch uses different wires, so it will not affect the speed. In a Gigabit Ethernet connection, 4 pairs of wires are used for data and power transmission at the same time, which can be done because the signaling in Ethernet is transformer coupled. The DC power supply is added to the midpoint of the transmission transformer, which does not affect the data transmission. And PoE switch not only does not limit the speed, but also has beyond 1G port switch support to meet network expansion needs. For example, FS S5860-24XB-U PoE++ switch with multi-gigabit ports can support 4x 25G uplink, ensuring agile network expansion. Actually, the Internet speed is drastically affected by your ISP, the Internet backbone, the remote website server, traffic on your local node, and more.

PoE Switch Supply

Do PoE Switches Cost More?

Regarding the price of the switch, the price of the PoE switch is higher than that of the ordinary switch. But in the long run, PoE switches will help you save money. By integrating the power supply into the switch, the PoE switch eliminates the need to purchase a power injector, which can save hundreds of dollars in power costs. In addition to cable costs and outlet costs, the installation cost is relatively low because the installation is quite simple, and you don't need IT teams to do the job. For PoE switches with 24-48 ports, the price will be much higher. But a switch with fewer ports is an excellent choice for small and medium-sized businesses that are both cost-effective. This is why PoE switches are recognized as cost-effective.

Do PoE Switches Have a Problem With Power Consumption?

The answer is no. It's understandable for engineers to worry about the power dissipation problem since signal integrity and power consumption is quite important. However, with the IEEE 802.3 specifications, PoE switches can meet the requirements of most engineers. For example, the IEEE 802.3bt specification mandates that delivering 90 W of power requires the use of all four twisted pairs within the cable. The maximum cable length is 100 meters. When using only two twisted pairs (pair set) to deliver power, the maximum DC loop resistance of the pair set shouldn’t exceed 12.5 Ω, which is guaranteed by using a Category 5 cable or higher. Thus, there won't be any issue of power dissipation if the cable requirements are met. If you want more details, you can click the article: PoE Switch Power Consumption: More Electricity Cost?

Does New Standard Switch Only Support New Powered Devices?

To meet the demand for higher power, the IEEE released a new PoE standard at the end of 2018, to significantly increase capacity. IEEE 802.3bt allows for up to 60 W to 100 W of power at the source. At this time, some users may be concerned about whether the new standard requires new equipment. The answer is no. If you are a related industry practitioner, you might know that backward compatibility is quite essential, which is a property of a system, product, or technology that allows for interoperability with an older legacy system, or with an input designed for such a system, especially in telecommunications and computing. The IEEE 802.3bt specification is fully backward-compatible with IEEE 802.3af (12.95 W at the PD) and IEEE 802.3at (25.50 W at the PD), which allows a mixture of PoE standards to coexist in the same network. Therefore, the new equipment is not necessary.

Can Non-PoE Devices Be Used with PoE Switches?

The detection and identification function is present before the power supply in PoE switches that adhere to the standard (also known as an active PoE switch). The PoE switch will send a signal to the network when the device is connected to see if the IP terminal in the network has a powered device that supports PoE. If it supports PoE switches, the PoE switch will just power it; otherwise, it won't power anything. Therefore, you can connect a non-PoE device to a PoE switch, and only data will be transmitted.

PoE Switch Connection

How to Determine How Much Power PoE Switch Is Needed?

A switch's overall PoE port output power is restricted. The decision is often made based on the PoE switch's total power output power, the rated power needed by the powered devices, and the necessary number of ports. When several PD devices need to access power, you must decide in advance whether the PoE switch's total power supply output power can be more than the combined input power of all PD devices and whether it adheres to the necessary power level standard.

Consider a PoE switch that complies with the 802.3at standard and has a total output power of 130W for 8 ports. The maximum output power of a PSE device per port is 15.4W under the 802.3 af standard, so the switch can connect all 8 ports to PDs that adhere to the 802.3 af standard. The PSE device can only access up to 4 802.3at devices that require a 30W power supply because the 802.3at standard states that the PSE device must output a maximum of 30W per port. Therefore, in order to avoid the issue of insufficient power supply caused by the device's inability to carry its load in accordance with the standard, the selection process should pay special attention to whether the total output power of the PoE-powered device meets the demand in addition to the standard compatibility and the number of interfaces.

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