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Wael, TR 42.7 is basically a cabling related organization, where the cable manufacturers are definitely under represented - compared to the connector manufacturers. Furthermore the cable heating touches a field way out of TIA 42.7's competence area, and these are code related issues. What we have to come up with is a scaling up of the difference between operating and ambient temperature, and we will have to ensure that this will be reflected in the relevant codes to make it legally viable.. Operating and ambient temperature were assumed to be equal in the past, but even under PoE (and here I have to make an apology for the negligence of myself and ISO/IEC JTC1/SC25 WG3, because we did not see and did not correctly evaluate the implications of even transmitting a current of 0.175 A over the data grade cables at that time) and especially under PoEP conditions these difference will have to be revised and possibilities will have to be evaluated for installation practices to eventually alleviate the conditions on this difference which will have to be imposed due to the number of cables in the bundles and the number of current loaded cables in this bundle - which was estimated by members of the PoEP task force to be close to 100%. As I do not see any comprehensive representation of the north American cable manufacturing industry and as I have serious doubts about the competence of the TIA TR47.7 group to consider the heating problems of cables, I have to suggest to wait for the results of the ISO/IEC JTC1/SC25 - ; ISO/IEC JTC1/SC25 WG3 - and the IEC SC 46C WG7 meetings with the confirmation of IEC TC46, before taking any further steps. I wrote a test procedure for assessing the heating problem of cables, and published also to all relevant standards committees. So far I did not see it yet on the reflector of IEEE though, despite the fact that I send it in the the chair of the PoEP task force quite a time ago and additionally I contacted as well Mr. D. Law. I saw some tests carried out according to this procedure, and I saw also some test with a slightly modified test configuration, where the error assessment render the test nearly useless, by looping the cables at the ends without properly isolating them. Furthermore the ambient temperature has not been kept absolutely constant as required for any thermodynamical analysis. To adjust the results afterwards according to the measured ambient temperature does not take into account the time dependent heat transfer. I shoiuld like to remind that this problematic has to be reflected in the nationally relevant codes, and that an absolute rigurus test method and procedure has to be maintained. Any short-cut in this sense jeopardizes our efforts in this direction ! Kind regards to all of you Jo Walling Chair of the UL-CSA Harmonization Committee for UL 444/CSA 22.2 No.214-02 Canadian head of delegation to ISO/IEC JTC1/SC25; IEC TC 46; IEC SC 46C and IEC SC48B Wael Diab wrote:
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