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What Is a PoE Injector and How to Use It?

October 14, 2019

PoE (Power over Ethernet) technology, capable of delivering power and data simultaneously on twisted pair Ethernet cabling, has earned itself great reputations by improving network agility and scalability in an efficient way. There are various styles of PoE devices, such as PoE switch, PoE injector, PoE splitter, etc. This article will focus on the PoE injector covering the definition, working principle, types, and installation.

What Is a PoE Injector?

A PoE injector, also called midspan or PoE adapter, can be implemented to make a non-PoE compatible switch work with PoE devices by powering compliant devices over a single Ethernet cable, which is perfect for low-power devices that need to be set up in locations where a power outlet is unavailable. It thus enables more flexibility by offering access to install devices in hard-to-reach areas, with a minimal impact on existing structures and budgets.

Here are some distinct benefits of PoE injectors:

  • Ease of installation: simply connect the PoE injector to the PoE endpoint and to an Ethernet switch to provide data and power.

  • Flexible to network expansion: PoE injectors add PoE capability to non-PoE Ethernet switches, which extends the network connection distance and provides combined power and data over Ethernet cable to end devices for a better connection.

  • Minimal investment budget: Utilizing the existing Ethernet equipment and cabling infrastructure, the relevant costs will be minimized in a PoE injector solution.

How Does a PoE Injector Work?

When Ethernet switches or other devices have no PoE function but need to support PDs (Powered Devices) like PoE IP cameras, PoE wireless access points (WAP), PoE lighting, etc., a PoE injector can help transfer both power and data to these PDs up to 100 meters. Usually, a PoE injector converts the alternating current into the direct current so it can be the power supplier for low voltage PoE devices.

PoE Injector Working Scenario

Types of PoE Injector

Active vs. Passive PoE Injector

A PoE injector follows the PoE standard IEEE802.3af, IEEE802.3at, or IEEE802.3bt, which is considered to use active PoE. 802.3af/at/bt as a handshake between the power sending and receiving PoE devices. The PoE injector won't power up if the receiving device doesn't provide the proper acknowledgment. This means that the 802.3af/at/bt injector will check the power coming in and if the power doesn't meet the device requirements it won't get powered up, ensuring the safety of the PoE device. Normally, 802.3 af/at/bt PoE voltage will always be 44 to 57 volts DC.

A passive PoE injector is usually a PoE injector adopting PoE technology that does not conform to the 802.3af, 802.3at, or 802.3bt standard. Passive PoE devices usually run on 18 to 48 volts DC. If the wrong voltage is connected, it may cause permanent electrical damage to the device.

12V vs 24V vs 48V PoE Injector

PoE injectors can mainly be divided into 12V, 24V, and 48V according to the output power voltage they can provide. When purchasing a PoE injector, you need to consider the voltage of it with the voltage standard of the PoE device which needs to be powered. Actually, in addition to the two categories above, the PoE injector can also be divided according to the port numbers, such as one-port PoE injector, 8-port PoE injector, etc.

How to Use a PoE Injector?

PoE injector excels in sending data while providing PoE to standard-based PoE, PoE+, and PoE++ compliant devices. In a practical application scenario, a PoE injector functions as an intermediary to connect non-PoE switch and PoE compliant devices. The devices like IP cameras or WAPs will be powered by the PoE injector.

How Does a PoE Injector Work.jpg

Take an IP camera as an example, the powering steps will be illustrated in the following. All you need is IP cameras, PoE injectors (depends on the number of powered IP cameras), standard network switch and Cat5e, Cat6 or Cat6a Ethernet cables.

1. Test all equipment to ensure the IP camera, PoE injector, and the management of the camera is working. Make all video and network configurations before mounting the IP camera.

2. Plug the Ethernet cable into the PoE injector's Power/PoE port and into the IP camera's PoE port.

PoE injector with IP camera.jpg

3. Mount your IP camera in the place where adequate light is available so it could capture a clear image on the screen.

4. Plug another Ethernet cable to connect the injector's Ethernet/Data port and the Ethernet switch.

PoE injector with non-poe switch.jpg

5. Plug injector power cord into a local AC electrical outlet.

Here is a guide video for your better understanding visually of the use of a PoE injector.

Considerations for Buying PoE Injectors

Before buying a PoE injector, you need to make sure whether it's right for you. So what makes the right PoE injector? You need to consider these three aspects before making a choice.

  • Number of PDs: If there is only one PD, a single-port PoE injector is enough. For several PDs, the number of PoE injector port must match with the injectors'.

  • PoE port power supply – PoE vs PoE+ vs PoE++: Make sure your injector's PoE standard is compliant with your PDs. There are three main PoE standards –802.3af (PoE), 802.3at (PoE+), 802.3bt (PoE++). They support a power supply of up to 15.4 W, up to 30 W, and up to 60 W /100 W respectively.

  • Power supply voltage: Make sure your PoE injector's voltage is compliant with your powered devices. For example, most of the security PoE cameras use 12 or 24 volts. Always check the specification of your PoE injector power supply to match the ones in your cameras to avoid overloads or operating issues.

PoE Injector FAQs

Q: Can I use a PoE injector to power a Gigabit switch?

A: The answer is no unless your switch has a port to allow for PoE power.

Q: What kind of cable do I need?

A: PoE injectors are based upon the rules defined by the IEEE 802.3 standards. Normally, Ethernet cables like Cat5, Cat5e, Cat6, etc. are all available to connect between the injector and the PoE devices/network switches.

Q: Does a PoE injector have manageable ports?

A: The PoE injector doesn't have manageable ports. PoE injectors can directly supply power to PoE PD through power source, plug and play. It has a short-circuit protection function and can directly supply DC power to wireless network devices and surveillance devices. If you need a management function, you could choose a PoE switch.

Q: Is using a PoE Injector safe? Will it damage my equipment?

A: IEEE 802.3af/at/bt compliant PoE injectors won't damage any equipment even if the equipment is not designed for PoE applications. The injector initiates a handshake procedure before it sends any power to the connected PD. That procedure utilizes low voltage and is harmless to any connected device, PoE, or non-PoE. Once the handshake is completed, the PoE injector begins sending power and triggers the connected device to start up. Should that handshake not complete successfully for any reason, the PoE injector will never send any power. It is this built-in feature of all IEEE 802.3af/at/bt-compliant devices that makes the technology so inherently safe.


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