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New Standards for Power over Ethernet

Fifteen years ago Cisco systems were the first to deliver power as well as data along Ethernet cables, connecting the 4/5 (+) and 7/8 (-) untwisted pairs to a power supply. The repurposing of these wires left both manufacturing processes and IT architecture in place, while delivering a massive increase in available functions. This developed into the ‘PoE Plus’ standard, IEEE 802.3at-2009, increasing the amount of power available and putting millions of units of network equipment on PoE power. Additionally, the single cable kept power loss to a minimum.

A further version, 802.3bt, has now almost doubled output again. By using all four pairs of balanced twisted-pair cabling at least 49 watts can be delivered to devices. This would put the estimated size of the market at 100 million powered devices. Given the inherent advantages of using existing technologies to supply new functions, one of the objectives of the IEEE 802.3 working group was to ensure a degree of backward compatibility while keeping capacity and demand in better alignment. That said, compliance to safety codes on extra low voltage circuits means that cabling needs to be, minimum, category 5e or higher.

The different categories of cable; 5e and 6, etc. refer to the degree of insulation and therefor amount of power an Ethernet cable can carry. In our experience, as a cable contractor in Phoenix, protecting equipment and people is often as simple as making sure that the correct cabling is supplied. One important safety feature is the use of an isolated power supply: the lack of physical boundaries between the user and the PoE voltage source, mean that spikes and short circuits are potentially dangerous. Safety certification may depend on 1500-V ac or 2250-V dc isolation. New standards for PoE, mean that cabling infrastructure, supporting wifi for business and internal connectivity may need a review. Enhancements to existing PoE standards need to be compatible with 10BASE-T, 100BASE-TX, 1000BASE-T, and 10GBASE-T is the ideal standard. Interfaces should remain unchanged.

The application, then, is vast: medical equipment, surveillance equipment, AV equipment ranging from conference rooms to intercoms, access points for wireless for business, IP cameras, manufacturing equipment, Network Time protocol clocks, keyless entry systems, retail points of service, digital signage, and multichannel WAP, to name but a few.

For network managers and experts such as CTS Cabling, determining the suitability of four-pair PoE networks needs to include the following considerations: the needs of the overall network, potential limitations of thermal capacity, and cabling and deployment strategies. While this can appear daunting, the driver for these changes remains economic: delivering power and data together saves millions on the installation costs of separate lines.

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