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Essential guide to pick a PoE Injector

Do you get any challenge to figure out how to power your IP devices, such as wireless access points, VoIP phones, and IP cameras? These pieces of equipment require communicating network and power source to bring it up. The convention switch only provides the network for communicating but no power. There is still a power supply problem you will need to deal with.

The power over Ethernet (PoE) technology allows single Ethernet cable to transmit power and data to your remote IP devices. Both PoE switch and PoE injector are able to add the power to a single Ethernet cable. If you already have an existing non-PoE switch and only have a desire of adding PoE to the network, PoE injector(or midspan injector) is a good choice to solve the power supply problem instead of purchasing a new PoE switch.

If you are a green hand in shopping for PoE injectors, you must be overwhelmed by the technical features available as well as be confused with various optional products. So in order to select a cost-effective PoE injector, somethings that you should pay attention to and understand


First of all, let’s understand the concept of PoE. Like we mentioned previously, the PoE utilizes a single Ethernet cable to provide both data connection and electric power to your powered devices (PD) such as wireless access points, IP cameras, and VoIP phones. This feature allows remote devices to be powered with no need of a separate power supply or an electrical AC outlet nearby.

Therefore PoE injector(Midspan) is a type of PSE(Power Source Equipment), which injects power without affecting the data through Ethernet cable(Cat 5e/Cat 6).

There are two types of PoE injector, passive PoE injector and active PoE injector.

  • Passive injector

In the common “passive” PoE system, 2 twisted pairs (4 wires) in Ethernet cable are simply merged into two wires to transport the electric power from an external power adapter.

While an active injector is integrated with a power source with the voltage and wattage are determined by the injector.

In addition to, active PoE injector also divides into standard and non-standard type. What’s the difference is whether the injector and the powered device have some protocols in common or not. The standard PoE injector complies with three standards, namely, IEEE 802.3af, IEEE 802.3at or IEEE 802.3bt power negotiation protocols while non-standard PoE injector transmits power to the powered device without negotiation of its required voltage or wattage from remote ip devices, and merely supplies power at all times, that is why it is also known as “always ON”.

This below are some tips for selecting a suitable PoE injector.

  • Tip one: Confirm the Voltage

You should check the maximum input voltage of the PoE powered devices and the output voltage of the PoE injector, in case that they fail to match. PoE injector has different types in accordance with the output power voltage, generally dividing into 12V, 24V, 48V. Technically, higher voltage injector can be used in farther distance, because the voltage will drop down sharply along with the increasing distance.

  • Tip two: Estimate power budget.

You should estimate the power of the PoE powered devices required, preventing unnecessary waste in purchasing a high power budget injector. As we know, power consumption exists during the power transmission. So distance should be taken into consideration. You are supposed to pick an injector with a little higher power than your powered devices need.

  • Tip three: Try not to use passive injector if possible.

Although passive injector is low cost, it is unsafe for people without basic technical knowledge.


  • Passive PoE injector

This is the common passive PoE injector you can find in the market, most of them are unbranded products. It may have different color or shape, technically it works exactly the same. Two twisted pairs into two cables to transmit low voltage power. As we know, only 2 twisted pairs are being taken to transmit 10/100mpbs fast network, leaving 2 spare twists to send the power. The passive PoE switch doesn’t support a gigabit network which needs all 4 pairs to transport the data. If passive PoE are used with gigabit networks, the bandwidth will slow down to 100mbps fast network automatically. The passive PoE usually works in pairs, a passive splitter is required at the remote end to separate the power wire from Ethernet cable. As no power negotiation and protection, the passive PoE system only can handle the low voltage and the short distance power. If the cable is too long, such as 30 meters, some of the power will lose on the cable which is converted to heat, the remaining voltage may become too low to supply you IP devices. Why are passive PoE still popular? Except for cost-effectiveness, the passive PoE accepts the external power adapter. If your front-end device needs some uncommon voltage from its custom power adaptor, you may need the passive PoE system to take in the power from its original power adaptor.

Tips: switch off the system power before making any connection. As zero protection with passive injector, the plug in process during the connection may create power surge and damage your remote devices.

Voltage: depends on external power source

Watt: same as voltage

Distance: less than 15 meters, even shorter

Power negotiation: NO

Short Circuit protection: No

Overload protection: No

Power surge protection: NO

  • Active PoE injectors

non-standard PoE injectors

The second type is 24VDC/48VDC non-standard active PoE injectors. Why we said no standard because these injectors don’t follow any specification such as IEEE802.3 which requires power negotiation before releasing the power. properly there is no protection as well. The ieee802.3 introduces two verification steps also named PD signature. Firstly, the Injector sends low voltage (5V) to the front end IP device meanwhile measures the current feedback. If the return current is right, the injector will go to step 2 to classify the ip device to determine what the maximum power the injector should provide. The non-standard injectors have none of these protocols. One of the reasons is both the injector and splitter need a chipset to complete the PD signature process. At the beginning, different manufacturers were facing the compatible issue even both injector and splitter claim to be IEEE802.3 standard products, because the return signal has been set to different values in the above power negotiation process. In this case, the Non standard injector may skip the compatible issue because it sends the power once the injector is plugged in an AC outlet. Of course, it is not a safe operation. Ubiquiti is one of exceptions who provides non-standard PoE injector but still adds the protection to the injector. However these products may doesn’t power standard PoE IP devices.


The mainstream injector is compatible with ieee802.3 standard now. The benefits of standard PoE products are plug and play. Basically need no concern to the voltage and distance. What you need to choose is the power budget. There are three standard IEEE802.3 af/at/bt.

IEEE 802.3af

This IEEE 802.3af (PoE) standard supports the delivery of power up to 15.4W, offering DC 48V power over Ethernet cables. The 2nd classification step we mentioned above can determine the maximum power transport over the Ethernet cable. This suits the powered devices such as wireless access points, IP cameras, and VoIP phones. According to the distance between the PoE injector and the powered devices where you want to set up should be less than 100m as voltage will sharp down.

Voltage: 48V

Watt: 15.4W

Distance: within 100m

Power negotiation: IEEE 802.3af

Short Circuit protection: Yes

Overload protection: Yes

Power surge protection: Yes

IEEE 802.3at

The IEEE 802.3at (PoE+) standard increases the power up to 30W. The remaining power budget is set to 25.5W at the splitter, which delivers around 2 times power to remote devices. It benefits the high power demanding equipment such as PTZ camera, access control. Both PoE and PoE+ have been in the market for more than 10 years. There were compatible issues at beginning especially for PoE+ because the PD signature process requires more precise feedback value. Now most of the PoE injectors are compatible with PoE and PoE+.

High power 30W power Capability

PoE extender

quick and easy install

Power source integrated – All in one


IEEE 802.3bt

The IEEE802.3bt PoE injector is a new standard which is capable of output 90W maximum power. Similar as a few years ago when PoE+ (30W) appeared, only a few 90W PoE injector are available in the market. You need to choose 90W PoE splitter to match the injector as the splitter module is not integrated in the front devices yet. The ieee802.3bt employs 4 twisted pair ethernet cables to transport the power and data. The remaining power budget is set to 71W.  This can benefit the power hungry device such as LED lighting, PTZ camera, Point of Sale terminals, touch screen computer. The IEEE802.3bt injector uses a dual PD signature verification process. The first Pd signature will verify it is backwards compatible with PoE and PoE+, after first signature pass, it moves to second signature which means there are two power negotiations before releasing 90W power. Another similar protocol but doesn’t belong to ieee802.3 is AoH which can injector 95W power, the remaining power budget is 72W. The 100W is almost the limit power over single Ethernet cable. In order to bring up the power, either increased voltage or current will create a safe issue which fails to meet the regulation. The next technology is the digital power which can transport higher power budget safety. The below is the video about the 95W PoE system which supports both IEEE802.3bt and PoH standard.

Advanced next generation PoE

All-in-One touch PC

95W 4 pairs

intelligent LED indicator for real time

Ultra PoE splitter

PoH Power over HD-Based-T 95W

3X power

Leave a comment below if you have any questions.

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