Photo courtesy of Olivander
1. What is PoE – Power Over Ethernet?
Power over Ethernet (PoE) does exactly what it says — it carries power over ethernet cables. So, an ethernet cables caries both data and current together to operate devices like wi-fi access points. This is very helpful to install wi-fi access points in ceilings, where it is hard to find power outlets. Only smaller devices can be powered using the PoE, as it carries limited power over the ethernet.
2. How does PoE works?
Following are the terminologies used in the PoE network:
- PD – Powered Devices: PDs are end devices that can accept the power transmitted over Ethernet Cat-5 cable.
- PSE – Power Source Equipment: PSEs add power to the ethernet cable.
- Midspan device: These are power injectors that stands between the standard ethernet switch and the end device.
- Endspan devices (PoE Switches): These are Ethernet Switches that includes the circuit to inject power to the ethernet cable.
Cat5 ethernet cable has 4 twisted pairs. Out of 4 pairs:
- 2 pairs are used for data transfer,
- 2 pairs are spare and not used.
There are two approaches to transfer power over ethernet.
Approach 1 uses data pairs:
The same 2 pairs used for data transfer, is used to carry power. The PSE injects power to the 2 data pairs (pin 1,2 and pin 3,6) via the center tap of the transformers without affecting the data transfer.
Approach 2 uses the spare pairs:
The 2 spare pairs that are not used, is used to carry power. It applies +ve voltage to pins 4 and 5 of ethernet cable. It applies -ve voltage to pins 7 and 8.
3. What are the Benefits of PoE?
- Portability: Install end-devices where it is hard to get power. For example, you can install a wireless access point in the ceiling, where you cannot find power outlet.
- Cost Savings: For a large scale deployment of wireless access point, you don’t need to install power outlet for the access points, which can be a huge cost saving.
- Simplicity: You need to run only ethernet cable to the end devices, which eliminates the cable clutter.
- Safer: No AC power is involved, as you don’t need to install A/C power outlet for the end-devices.
- Easy Maintenance: You can restart the end-device remotely. No need to press the power button to reset the equipment. You can easily move the end-devices wherever you can lay a LAN cable.
4. Sample List of Equipments that uses PoE.
- D-Link Power over Ethernet (PoE) Adapter – DWL-P50
- D-Link Power Over Ethernet Adapter – DWL-P200
- Linksys Power Over Ethernet Adapter Kit
PoE Wireless Access Point:
PoE Network Surveillance Camera:
- Airlink Power over Ethernet Network Camera – SkyIPCam310
- Panasonic 21x Optical Zoom Pan/Tilt Network Camera – BB-HCM580A
- Mobotix Outdoor, Wide Angle Lens, Motion Detection Camera D22M-IT