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Networking / Power System / What Is a PoE Injector and How to Use It?

What Is a PoE Injector and How to Use It?

Posted on By FS.COM

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 Gigabit PoE switch, PoE injector, PoE splitter, etc. Here we will focus on addressing everything you want to know about PoE injector including what it is, how it works and how to use it.

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 such as Cat5e, Cat6, Cat6a, etc. It 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 budget.

We could benefit from using PoE injector in these ways:

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

  • 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.

  • Investment protection: PoE injector protects the investment by utilizing existing Ethernet equipment and cabling infrastructure, with minimal impact on the budget.

Types of PoE Injector

Active vs. Passive

If your PoE injector uses the PoE standard IEEE802.3af or IEEE802.3at (or the newly released IEEE802.3bt), it is considered to use active PoE. 802.3af/at/bt does a handshake between the power sending and receiving PoE devices and won’t power up if the receiving device doesn’t provide the proper acknowledgment. This means that the 802.3af/at/bt 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 that uses PoE 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 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, 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.

How Does a PoE Injector Work.jpg

How to Use a PoE Injector?

PoE injector excels in sending data while providing PoE to standard-based PoE and PoE+ compliant devices. If you have a non-PoE switch, a PoE injector could be used to power devices like wireless access points. Here we illustrate the steps for powering IP camera (it could be other PoE enabled devices) with a PoE injector and a non-PoE network switch. 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 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.

Otherwise, you can refer to the video below to learn how to use a PoE injector.

Considerations for Buying PoE Injectors

Before buying a PoE injector, you need to make sure 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+: Make sure your injector’s PoE standard is compliant with your PDs. There are two 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: Can you tell me if a PoE injector has manageable ports?

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