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A guide to PoE injectors
A Power-over-Ethernet (PoE) injector is an adapter designed to send power down an Ethernet network cable in order to power PoE-compatible network devices. It is only required when a PoE-powered device (such as a wireless access point or security camera) is plugged into a non-PoE switch or router.
There are two very different types of PoE injector to be aware of: -
- Passive PoE Injectors can be thought of as 'dumb' injectors - They send power down the network cable regardless of what current the device requires. Available in either 28V or 48V options, as there is no negotiation between the device and the injector it is imperative that the correct passive injector is only used on devices that specifically state compatibility with passive injectors of this voltage.
Warning: Connecting a passive PoE injector to an incompatible PoE device could cause permanent damage to the device.
- Active PoE Injectors are 'smart' injectors - Only a small current is sent down the cable initially - enough to establish how much power the device needs to operate correctly. The injector then sends this exact amount down the cable. Because of this negotiating process there is very little risk of damaging a PoE device by using the wrong active injector. Active PoE adapters conform to IEEE standards 802.3af, 802.3at or 802.3bt (see below).
Within active PoE, there are currently 3 main IEEE standards, each with different power capabilities: -
Because of the smart negotiation involved in active PoE, injectors and switches that conform to these standards are backwards compatible with previous standards - For example a PoE++ switch can power a mixture of PoE, PoE+ and PoE++ devices.
Finding the right PoE injector
It is important to make sure you select the right injector with your device. Supplying a PoE+ device with only a PoE adapter will result in a device not powering up (or operating incorrectly) - or worse, connecting a passive injector to a device that only supports active PoE could permanently damage the device.
If you're not sure what PoE requirements your device has, take a look at the product datasheet from the vendor. It should state whether your device confirms to 802.3af, 802.3at or 802.3bt - or alternatively if it requires a passive injector.
Installing your PoE injector
There are two RJ-45 Ethernet ports on the PoE injector - One is to connect to the switch, and the other is the powered output to go to the PoE-powered device. The PoE injector then connects to the mains. The placement of the PoE injector depends on your scenario but it's important to note that the maximum cable length for PoE is 100m.
At the switch end
At the device end
Some popular PoE injectors currently in stock...
Ubiquiti POE-24-12W-G 24V 12W Gigabit Passive PoE Injector - 24V (12W Max) see details
£8.66 ex. VAT
£10.39 inc. VAT
Manu. part ID POE-24-12W-G
Ubiquiti POE-48-24W-G Gigabit Passive PoE Injector - 48V (24W Max) see details
£10.24 ex. VAT
£12.29 inc. VAT
Manu. part ID POE-48-24W-G
Ubiquiti U-POE-at Instant 802.3at 48V 30W Power POE Injector, delivers up to 30W of PoE+, compatible with the U6 LR, U6 Pro, and other 802.3at PoE+ devices, surge and clamping protection, AC cable with earth ground see details
£11.24 ex. VAT
£13.49 inc. VAT
Manu. part ID U-POE-AT
TP-LINK TL-POE150S - PoE injector, External, 48V, 1 x RJ-45, IEEE 802.3af compliant, Up To 100 Meter
TP-Link TL-POE150S - PoE injector, External, 48V, 1 x RJ-45, IEEE 802.3af compliant, Up To 100 Meters see details
£11.37 ex. VAT
£13.64 inc. VAT
Manu. part ID TL-POE150S
Ubiquiti U-POE-af Instant 802.3af 48V 15W Power POE Injector see details
£11.47 ex. VAT
£13.76 inc. VAT
Manu. part ID U-POE-af
TP-Link TL-POE160S Power Over Ethernet PoE+ Injector (802.3at/30W) see details
£13.19 ex. VAT
£15.83 inc. VAT
Manu. part ID TL-POE160S
£38.31 ex. VAT
£45.97 inc. VAT
Manu. part ID TL-POE170S
Gigabit High-Power PoE+ Injector, 1 x 30 W, IEEE 802.3at/af Power over Ethernet (PoE+/PoE) (UK Power Cord) - 120 V AC, 230 V AC Input - 1 x 10/100/1000Base-T Input Port(s) - 1 x 10/100/1000Base-T Output Port(s) - 30 W see details
£39.86 ex. VAT
£47.83 inc. VAT