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What is the Basic of Power Over Ethernet?

Power over Ethernet (PoE) is a technology that allows the transmission of both power and data over a single Ethernet cable. This innovative solution simplifies installations, reduces costs and provides flexibility in where devices can be placed. In this blog, we will delve into the basics of PoE and how it works.

Everything You Need to Know About PoE


Let’s start by understanding the key components of PoE. The two main elements are the power sourcing equipment (PSE) and powered device (PD). The PSE generates electrical power and sends it to the PD, which consumes the power to run the device. These devices can vary from VoIP phones and wireless access points to security cameras and IoT devices. Moreover, the PSEs can be further divided into endspan and midspan depending on how they supply power to devices. Endspan refers to Ethernet switches that are designed to supply power directly to PoE-enabled devices without the need for any additional equipment, such as the PoE switch. On the other hand, midspan refers to a PoE injector that is installed between the Ethernet switch and the PD. It’s often used in situations where an existing Ethernet switch does not have PoE capabilities, or where additional power is needed beyond what the switch can provide.

What’s Power Budget? PoE Standards?


The power budget refers to the maximum power a PSE can deliver to all connected devices simultaneously. This ensures that the PSE does not overload and cause power disruptions. Before implementing PoE, it’s important to calculate the power requirements of all connected devices. The most common standards are IEEE 802.3af and IEEE 802.3at, also known as PoE and PoE+. The key difference between the two is the amount of power they can provide. IEEE 802.3af can deliver up to 15.4 watts of power, while IEEE 802.3at can deliver up to 30 watts. This allows PoE+ to power devices with higher power requirements, such as pan-tilt-zoom (PTZ) cameras.



How does PoE Work?


To transmit power and data together, PoE utilizes unused wires in the Ethernet cable, specifically the spare pairs. Traditionally, Ethernet cables consist of four twisted pairs, but modern Ethernet networks only require two pairs for data transmission. This leaves the other two pairs free for PoE power transmission. By using the spare wires, PoE does not interfere with data transmission or the network’s performance. To implement PoE, both PSE and PD must be PoE-compatible. The PoE switch or PoE injector can automatically detect if a connected device requires power and, if so, supply it accordingly. Likewise, PDs must be designed to accept power over an Ethernet connection. If a device is not PoE compatible, an external PoE splitter or injector can be used to convert the power from an Ethernet port into a usable DC power supply for the device.

What Are the Benefits of PoE?


First and foremost, PoE simplifies installations by eliminating the need for additional power cables. PoE also provides flexibility in device placement, allowing devices to be installed in locations where power outlets may not be readily available. Additionally, PoE enables centralized power management and monitoring. PSEs can remotely monitor the power consumption of connected devices, allowing for better energy management and troubleshooting. This capability also facilitates easy device rebooting if necessary, without the need to physically access the device.

What Are the Drawbacks of PoE?


One of the main drawbacks of PoE is limited to a range of around 100 meters, which may not be enough for larger buildings or outdoor installations. Another drawback of PoE is the potential for power loss. As power is transmitted over the Ethernet cable, there is the potential for power loss due to cable resistance, which can reduce the power available to the device. This can be mitigated by using high-quality cables and PSE, but it is still a consideration. 

Is PoE Safe to Use?


PoE is generally safe to use when implemented correctly. However, like any electrical system, PoE does carry some risks that need to be considered. One of the potential hazards of PoE is electric shock. If the cabling used for PoE is damaged or frayed, it can become a safety hazard. Additionally, if the connected device is not designed to handle the amount of power being supplied through PoE, it can cause damage or create a safety hazard. Another potential concern is that PoE can generate heat, which can damage connected devices if proper ventilation is not provided.

However, these risks can be mitigated through proper installation and use of PoE equipment. For example, it’s important to use properly rated cables and connectors, and to make sure that the equipment is installed in a well-ventilated area. And you can opt for active PoE instead of passive PoE. Active PoE refers to a type of PoE that uses a negotiation process between the PSE and the PD to determine the amount of power that should be delivered, ensuring that the connected device receives the appropriate amount of power and reduces the risk of damage or safety hazards.



Which Type of Cable Should I Use?


When it comes to PoE installations, it’s generally recommended to use solid copper cables rather than copper-clad aluminum (CCA) cables. This is because CCA cables have a higher resistance than solid copper cables, which can result in more power loss, lower voltage and potentially higher temperatures. This can reduce the efficiency of the PoE installation and increase the risk of damage or safety hazards. The two most common types of pure copper cable used for PoE are Cat5e and Cat6 cables. Cat5e cable supports data rates of up to 1Gbps, while Cat6 cable is rated to handle up to 100 meters of cable length and supports data rates of up to 10 Gbps.

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