December 2, 2022

PoE Injectors Bring Plug-and-Play Power to Industrial Network Devices


  • By Henri Martel
  • August 12, 2022
  • Antaira Technologies, LLC – formerly Aaxeon Technologies
  • Characteristic

PoE Injectors Bring Plug-and-Play Power to Industrial Network Devices

Power over Ethernet (PoE) LAN switches are essential components of modern industrial networks, providing DC power to an assortment of PoE (PD) powered devices over long distances, while transmitting data over the same CAT5 cable or superior. Managed or unmanaged, PoE LAN switches offer a number of important benefits to network administrators. For example, without being tethered to electrical outlets, connected PDs can be positioned in optimal locations during network expansions and easily repositioned when needed, improving network flexibility and scalability while saving on overhead. installation of power outlets. The latest version of the IEEE PoE standard, known as 802.3bt, increases maximum power to 90W per switch port, opening the door to powering PDs as diverse as LED lighting, sensors, WAP, alarm systems, IP PTZ cameras and monitors, and even air conditioners.

Since their introduction in the early 2000s, PoE LAN switches have heralded major changes for industrial applications and accelerated the already rapid transition to Ethernet-based industrial control systems. However, millions of non-PoE LAN switches are in use today without this capability. So what does a network administrator do when an existing Ethernet switch isn’t PoE-enabled but the PD they’re adding to the network is? In this brief article, we will explain how to overcome this lack with a simple device: the PoE Injector.

What is a PoE injector?

Essentially, a PoE injector works as a middleman to connect a non-PoE switch to PoE-enabled devices. It does this by adding power to an Ethernet cable so that any connected IEEE 802.3af, IEEE 802.3at, and IEEE 802.3bt PDs can receive power. Also known as Midspan or PoE adapters, PoE injectors are typically used with low-power (30W) devices installed in hard-to-reach places where no power outlets are available, although newer industrial injectors can deliver much higher powers up to 95W through multiple ports. Since many injectors must be installed outdoors or in factories, enhanced environmental features – such as IP30 enclosures, wide temperature ranges, shock, EMC and vibration resistance, lightning protection, overload protection and redundant power inputs – are often added to support zero downtime applications.

PoE injectors easily integrate with existing network switches. Mounted on a wall or on a DIN rail, the injector sits between the non-PoE LAN switch and the PoE-capable PD. The injector is networked to both the switch and the PD via Ethernet cables, and is powered separately from a local AC outlet which it automatically converts to DC. Midspans are typically configured with two unmanaged RJ45 ports: data in and data out + power. The data in port connects to the non-PoE LAN switch while the data + power out port connects to a PD which can be positioned up to 100 meters (328 feet). If there is only one PD to power, a single port PoE injector is sufficient. For multiple PDs, the number of PoE injector ports must match the injector. Additionally, a non-PoE gigabit switch will require a gigabit injector to maintain network speeds.


It is important to know the type of cabling to use when connecting PoE devices with the PoE injectors and the switch. According to the IEEE PoE standards, the cabling requirements for PoE injectors vary with each standard, for example, the IEEE 802.3af standard allows a maximum of 15.4 watts of power to be delivered, corresponding to Cat 3, Cat 5 or superiors. Similarly, IEEE 802.3at standards use Cat 5 cable, while 802.3bt Type 3 and 802.3bt Type 4 use Cat 6 or better cables due to increased heat and power transmissions.


All IEEE 802.3af/at/bt compliant PoE injectors are designed to prevent damage to a device even if that device is not designed for PoE. Once plugged in, a handshake procedure will be initiated by the injector before it sends power to the connected PD. This procedure uses low voltage and is safe for any connected device, PoE or non-PoE. Once the handshake is successful, the PoE injector starts sending power and triggers the connected device to start up. If the handshake is not completed for any reason, the injector will not send power, thus preventing damage.


To avoid overloads or malfunctions, the PoE-enabled PD must comply with the voltage supplied by the PoE injector. As mentioned earlier, there are three PoE standards – 802.3af (PoE), 802.3at (PoE+), 802.3bt (PoE++) – supporting up to 15.4W power, up to 30W, and up to 60W/100W respectively. For example, most PoE IP cameras use 12 or 24 volts. So check the specifications of the PoE injector to make sure they match the specifications of the camera, i.e. PoE or PoE+.

Active vs passive injectors

There are critical differences between an active PoE injector and a passive PoE injector. An active PoE injector, when connected, establishes the “handshake” with the previously mentioned PoE device, and if successful, powers the device. An active PoE injector will first determine the characteristics of the incoming power flow. After that, it matches the bitrate to the requirements of the device itself. If it detects an abnormality in the current flow, it simply will not flow current to the device. This eliminates the risk of burning the device.

Active PoE injectors comply with IEEE 802.3af, IEEE 802.3at and IEEE 802.3bt standards, while passive PoE injectors do not. A passive injector does not perform a handshake function. It will send raw, unnegotiated power down Ethernet cables to connected devices, whether they are able to handle it or not. This is why Passive PoE is nicknamed “Always ON”. To mitigate the risk of passive PoE, always ensure that you connect the device to the exact voltage required by the device.

When using a PoE injector to power devices, Antaira strongly recommends using an active PoE injector to supply power.

Benefits of using PoE injectors

Due to their ease of integration and PoE functionality, industrial PoE injectors have several advantages, including:

  • Ethernet cables connect the LAN switch to the PoE device, reducing cabling complexity in industries where deployment needs to be fast and reliable.
  • It eliminates the added cost of expensive power wiring.
  • It saves the expense of separate AC/DC power supplies dedicated solely to powering cables.
  • It reduces the need for bulkier cabling infrastructure.
  • Due to their compact size, industrial PoE injectors offer a practical solution for industries where there is a need to integrate and extend existing networks.
  • PoE injectors are available in different power configurations, making it easy to power devices with varying power requirements.

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