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Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10 - Power over Ethernet performance in industrial environments


Regarding your specific questions:

1. Noise interference with PoE detection.

Unconstrained noise will, of course, interfere with the detection process and may even cause a false detection. However, PoE was design to work on channels that are suitable for Ethernet communication. If the installation is compliant with the appropriate channel criteria (whether CAT-3, CAT-5 etc.) for the type of Ethernet interface required then the PoE scheme is very robust. Note that a compliant installation is not simply any installation that uses CAT-5 labeled cable, please read the relevant cable installation documents for further information.

If you have issues with media performance in an industrial environment then you should talk to a media standards development organization.

2. Coupled noise from PoE interfering with communication.

802.3, clause 33.2.8 has specific requirements on the power source regarding load regulation and noise; clause 33.3.5 has specific restrictions on powered device inrush, ripple and noise. Clearly the noise within these limits will have some (albeit small) effect on the communication but the onus is on the equipment manufacturers of systems that support PoE to ensure that their interfaces tolerate the increased noise within the specifications of clause 33. It is also part of the design challenge to ensure that whatever noise is generated from switching power within a system is coupled onto the interface within the limits prescribed.


IEEE 802.3 is a standards development organization. It does not offer consultancy, nor does it assess compliance of any implementation or installation. If part of the standard appears to be ambiguous then you may enter an interpretation request; if there appears to be a deficiency then you may enter a maintenance request.

In the meantime, I stand by what I wrote as a response to the liaison request.


Robert E Lounsbury wrote:

----- Message from Robert E Lounsbury <relounsbury@xxxxxxxxxxxxxxx> on Wed, 8 Jul 2009 06:38:06 -0400 -----
Hugh Barrass <hbarrass@xxxxxxxxx>
owner-stds-802-3-poep@xxxxxxxx, STDS-802-3-POEP@xxxxxxxxxxxxxxxxx
Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10 - Power over Ethernet performance in industrial environments

Hello  Hugh, Dave,

Please read the liaison letter.  Please disregard the damaged device.  The damaged device only served to start the discussion in IEC.  The letter is asking two very basic questions that might precipitate some considerations in the specification.  First Dave mentions noise coming from the device loads back onto the channel. This was one of the questions in the letter.  Dave alludes to violating the specification.  Please point to where in the specification where noise produced and coupled back to the PoE channel is defined, limited or otherwise discussed.  Second the letter asks if the PoE TG has considered analyzed what might happen if there is Radiated, conducted or other environmental noise in the area where the PoE system is installed might cause problems during the probing process. This has nothing to do with any design flaws of a product but merely the environment.  If you consider Industrial noise levels as defined by IEC out of the scope for 802.3at, then please respond indicating so. Then we might be in a position to disallow PoE in industrial.    Thanks for your time