Comments: Power over Ethernet requires connector evolution

Comments on the PoE+, IEEE-pending standard 802.3at, follow. Add your views below. See related links.

03/08/2007


Add your comments to the Power over Ethernet discussion

See other links and resources.

Connectors need to be redesigned if they're going to carry the higher power required by PoE+. So say readers of "

More Power over Ethernet

" ( CE , February 2007, p. 24), about the pending IEEE standard. Others respond.

Comments on the PoE+, IEEE-pending standard 802.3at, follow.

" One problem I see is the RJ45 Ethernet connector . The companies that offer PoE parallel conductors need to increase the current carrying ability of the connector. The other thing is the distance is limited by the wire size of the CAT 5 or Cat 6 cable. We were involved in designing a CCTV system for Park and Ride Mass-transit. We explored the possibility of using PoE. The problem encountered was the power needed to heat the outdoor dome and power the Pan-tilt-zoom cameras. The solution as I see it is the RJ45 Ethernet connector has to be redesigned to include a power connection that will handle at least 5 Amperes rated at 120 V ac or 24 V dc. Along with this connector a composite cable using shield twisted pairs for communication and power that will go 1000 feet or 300 m. If I had this I could have used a power injection module at the Ethernet Switch to power each camera."
James Bain of Elcon Associates Inc ., Portland, OR

" Two approaches under investigation : The RJ45 connector is being used to carry a max of no more than about 30 W at 48 V based on commercial standards. This most common implementation is being brought to the factory floor and it is limited by the gauge of the wire and contacts. This amount of power is not acceptable, and voltage above 30 V brings devices above the low voltage directives that are all familiar with, making instrumentation and simple devices subject to much more stringent requirements (more cost). There are two major approaches that are being pursued to solve this problem.

"Adaptations are being made to the RJ45 (and the cable that it is connected to) to allow it to carry more power. We have seen hybrid connectors with special power contacts accepted in some organizations, also some manufacturers adding conductors to the sides or top of the RJ45 jack and making special receptacles to receive this configuration. I do not believe this will be the winning solution.

"The other approach is to define a round style Ethernet connector (M12) with heavier gauge pins and wire to carry larger loads more suitable for the higher power we need in the factory. I think this has the chance to be the winning approach, but it is unclear right now and the standards are still evolving to create something that all can agree on. I would say that no approach is really broadly accepted yet and PoE on the factory floor (other than the 48 V low power option from the commercial market) is still a problem to be solved."

Ed Nabrotzky, general manager, industrial communications, Woodhead, a division of Molex , Waterloo, Ontario, Canada

See also other Ethernet power discussions and information:

- CIP networks: 24 V dc Power with Ethernet specification expected in April ; and

- Power over Ethernet Plus: Ideal for factory automation .





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