Power over Ethernet (PoE)

PoE has emerged as a popular technology that provides power and data to network devices on the same Ethernet cable.

All Powered Devices (PDs), including security network cameras, wireless access points (WAPs), building automation and control systems, and voice-over-IP phones receive the electrical power on the Ethernet cable from a network switch or power injector which are known as Power Sourcing Equipment (PSE). Only the PSE is connected to a power supply.

Why PoE?

PoE converges the electric power and communication control network onto a single infrastructure.

PoE is safe; it doesn’t require a dedicated mains power supply connection for end devices, which also reduces the total installation cost.

PoE switches provide clean, stable, reliable DC power.

Ethernet is a global harmonized standard and IEEE has been standardising PoE to reduce the likelihood of compatibility issues. Customers should be able to use the same products anywhere on the planet.

IEEE Standards

IEEE802.3af specifies output of 15.4W

IEEE802.3at specifies output of 25.4W

IEEE 802.3af and IEEE802.3at standard support two alternatives for power injection

  • Alternative A, where power is supplied via the center taps of the coupling transformers on data pairs 1/2 and 3/6.
  • Alternative B, where power is transmitted over pairs 4/5 and 7/8

Network elements compatible only with IEEE802.3af are classified as Type 1, and elements compatible with IEEE802.3at are listed as Type 2.

  • Type 1 (over two pairs) – The PSE can supply a maximum of 15.4 W over a voltage range of 44 to 57 VDC using Category 3 cabling or better.
  • Type 2 – The PSE can supply 30 W (over two pairs)

OSD products are designed to be compatible with Type 1 and Type 2.

Future of PoE

PoE++ = 60W up to 100W

PSE will supply power over all four data pairs.

Upcoming new standard IEEE 802.3bt possible classifications:

Type 3 (over four pairs) – The PSE can supply 40W to 60W over a voltage range 47-57VDC

Type 4 (over four pairs) – The PSE can supply 75W to 90W over a voltage range 47-57VDC

Why do we need this much power?

IP cameras with PTZ, heaters and blowers, and dynamic IR may require up to 95W PoE

Industrial lighting systems may require up to 90W.

Telecommunications Base Stations may require up to 75W PoE.

Important Note

  1. As convenient as PoE is, with products needing 60 to 100W of PoE, a power supply is still required which will support these high powers and the power supply will be much larger than the PSE in some situations.
  2. Until there is a ratified standard for PoE above 25.4W, care should be taken when using power above 25.4W as different manufacturers of Power Sourcing Equipment (PSE) and Powered Devices (PD) devices may have slight;y approaches to implementation of PoE++. Bench testing is recommended prior to site installation.

Future OSD PoE Products

90W PoE++

Media Converter – OSD2153HP

Ethernet Switches –

  • 6 Port OSD2251HP
  • 8 Port OSD2254HP
  • 10 Port OSD2258HP

Telco Media Converter – OSD2175HP