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Re: [8023-POEP] List of questions regarding cabling and connector s



Steve-

You are not correct for all cases, and therefore not for the worst case.

The worst case is 2 ports on a 802.3af PSE switch feeding a single 4 pair cable that is then terminated to two RJ-45s on a single outlet plate. Each outlet then goes to a separate PD.

This is a permissible configuration under ISO/IEC 11801 although it is not conformant to TIA.

This configuration was discussed in the meeting and is the basis of Jo's calculation.

I hope this helps.

Geoff


At 12:30 PM 9/14/2005 , Steve Robbins wrote:
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Regarding the issue of cable heating, I have a concern about Jo Wallings analysis.  In his supporting document, "walling_2_0905.pdf" the last sentence in the second paragraph states "...under the assumption that all pairs in all cables are energized with the same current."
 
This is a valid assumption for PoE Plus, since it appears very likely that we'll use a 4-pair system.  But Jo's assumption is invalid for 802.3af since only half of the pairs are carrying current.
 
So I think Jo overestimated the heat dissipation in the cables (for 802.3af) by a factor of 2.