Re: [8023-POEP] Liaison letter from IEC TC65/SC65C/JWG10

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If we ignore the specifics of the failed device as Bob suggests, I think it is easy to address the liason's concerns.

802.3 is mostly a feature specification, not a product specification - 802.3at makes it clear that the requirements are functional and are not substitutes for EMI and safety standards. A product specification might include 802.3 clauses (by reference) and many additional feature specifications, as well as the appropriate environmental requirements (MICE catagories), and so forth. As Geoff pointed out, there is little environmental information in 802.3 - leading me to believe that the implementer (product designer) must overlay the appropriate safety and environmental specifications for that particular product.

Maybe the right question from the IEC should have been "To your knowledge, is there anything in 802.3 clause 33, or 802.3 that would preclude ethernet from operating in a noisy environment?" This is similar to the intent that 802.3at does not preclude an implementation from meeting safety standards, however following only 802.3 does not imply an implementation will meet the safety standards.

I am sure there are over 50M PoE ports operating in the field, some of which are in industrial environments and functional. Since nobody on the committee itself raised the flag, and since this is the first external inquiry in 4 years, we can assume there is not a raging misdetection problem in the industrial environment out there. I take this as a proof that it is possible to implement 802.3 clause 33 in a manner that operates in the industrial environment. If someone in the task force (a PSE vendor) has applicable experience this would help. We can state this in a liason - 802.3 clause 33 does not preclude implementations that operate in noisy environments.

Evidence was provided that problems can and have occured. We suffer from a lack of facts here. Despite this, the consensus amongst the task force is that perhaps the implementation that damaged devices was suspect, there was a defect, or the hardware was used outside its environmental design intent. If the IEC could show us how to break the standard, I am sure we would jump at the opportunity to fix 802.3at.

The industrial community's concerns might be addressed if we added a note or caution to the PSE detection section that reminded the PSE designer to consider the appropriate electrical enviroment standards when implementing detection (and maybe MPS per Peter). We have notes elsewhere in 802.3at.

Shadi's email shows that existing standards recognize the requirement that devices be used in the manner intended by the maker, or alternatively this means that measures be taken to effectively ameliorate the environment to one the equipment was designed for.

So I am hoping it is possible to answer the liason and address their root concerns in a manner that is consistent with 802.3 practice by providing a little guidance to the PSE designer in this last draft of 802.3at. Explaining that 802.3 is a feature specification and not a product specification might clarify our position.

Regards,

Martin

Martin Patoka
Systems Engineering Manager
Texas Instruments
O: 214-567-5487
mpatoka@xxxxxx

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