The common mode crcut resstance unbalance (CMCU) calculaton based on mn. / max. conductor resstance values and par to par resstance unbalance measurements ncludng loop resstance evsed and extended verson of an orgnal document publshed on May 7, 006 The present s an nformal reply to a problem rased by the lason letter from ISO/IEC JTC/SC5/Wg3 to IEC SC46 on IEC 656-5 to 656-7 cables, concernng common mode resstance unbalance (CMCU) between pars n data grade cables, and shall be used as a base for future standardzaton. It s as such forwarded to:.) the secretary of IEC 46.) the secretary of IEC 46C 3.) the char of IEC 46C WG7 4.) the secretary of ISO/IEC JTC/SC5 WG3 5.) the VP of ICEA Communcaton cable secton 6.) the lason offcer of ICEA to the ASTM D9 group 7.) the char of TIA 4.7 8.) the char of the PoEP tas group In fact, n vew of some changes of requrements proposed n the latest versons of IEEE 80.3af and 80.3ar the followng wll have to be consdered for future standardzaton. However, t has to be clearly stressed, that the dervatons gven heren have to be taen not only nto account for all those cables standardzed n the future, but they should serve as well all those cable companes nterested to wor through ther past producton protocols n order to get an overvew on the performance of the nstalled base, to get an overvew of what lmts can be reasonably specfed.. The common mode resstance unbalance (CMCU) based upon the resstance unbalance defntons The followng assessment of the common mode crcut resstance unbalance (CMCU) s based upon the defnton of the par to par resstance unbalance accordng to IEC and smlar results are gven also based on the par to par resstance unbalance accordng to ASTM D 4566-005. In these cases the common mode crcut resstance unbalance (CMCU) s gven n terms of the maxmum and mnmum conductor resstance n each par. Alternatvely the common mode crcut resstance unbalance (CMCU) s expressed also n terms of the loop resstance and the conductor resstance unbalance of each par 43 Church, Beaconsfeld, QC, H9W 39, Canada (54) 695-80 or (54) 695-6063 Fax: (54) 695-80
. Calculatons based on the IEC defntons. Calculaton based on the IEC defnton and the mnmum and maxmum conductor resstance of each par a.) Assessment of all resstance unbalance measurements, usng the IEC defnton,.e.: max mn CU () + max mn That means the resstance of each conductor has to be measured, and then the resstance unbalance wll have to be calculated. b.) In the context descrbed above t s mandatory for hgh performance data grade cables to calculate the common mode crcut resstance unbalance. Ths value s calculated for the 6 possble par combnatons usng the followng equaton: CMCU, ( max + mn ) max mn ( max + ) ( + ) + ( + ) max () max mn max mn where the ndces and desgnate the par combnaton under consderaton,.e. these ndces may run from to 4 under the condton: and < (3).3 Calculaton based on the IEC defnton and the loop resstance and the conductor resstance unbalance of each par For the loop resstances L of any par combnaton par we have: + + (4) Hence we get: max mn + CU CU max mn + CU CU (5) 43 Church, Beaconsfeld, QC, H9W 39, Canada (54) 695-80 or (54) 695-6063 Fax: (54) 695-80
Hence we get for the common mode crcut resstance unbalance (CMCU), respectng the condton of Eq (3): CMCU, ( CU ) ( CU ) ( CU ) + ( CU ) (6) Obvously the CU values have to be taen nto account as straght values, not n percent. If we assume a maxmum specfed value for the conductor resstance unbalance, then we get: CMCU, ( CU ) Spec L + L Spec ( CU ) C, (7) where CL - s the loop resstance unbalance As a result we see, that the CMCU depends prmarly on the loop resstance unbalance, as the frst term of the rght sde of Eq (7) s approxmately.. Calculaton based on the ASTM defntons. Calculaton based on the ASTM defnton and the mnmum and maxmum conductor resstance of each par a.) The calculaton of the present CU assessment follows the defnton of ASTM D 4566-005 and may be consdered for the North Amercan customers. Ths defnton s as follows, and yelds resstance unbalance values approxmately twce as hgh as the IEC defnton: max mn CU (8) Frst the resstance of each common mode crcut conductor ( CMC ) and (that s the conductors of each par connected n parallel) has to be determned: 3 43 Church, Beaconsfeld, QC, H9W 39, Canada mn b.) To use the ASTM defnton of the resstance unbalance accordng to the ASTM D 4566-005 defnton, s slghtly more awward. The calculaton yelds two results, and the correct one has to be determned as follows: (54) 695-80 or (54) 695-6063 Fax: (54) 695-80
CMC max mn max mn CMC (9) + + max mn Then the calculaton of the two possble solutons I and II contnues: For: (0) CMC CMC We have CMCU I ( max + mn ) ( + ) max mn CMCUCMC, () max mn For: () CMC CMC We have CMCU II ( max + mn ) ( + ) max mn CMCUCMC, (3) max mn.3 Calculaton based on the ASTM defnton and the loop resstance and the conductor resstance unbalance of each par For the loop resstances L of any par combnaton par we have as n Eq (4): + + (4) Hence we get: max mn + CU + CU + CU max mn + CU + CU + CU (5) Hence we get for the condton accordng to Eq (0): 4 43 Church, Beaconsfeld, QC, H9W 39, Canada (54) 695-80 or (54) 695-6063 Fax: (54) 695-80
CMCU, Dr. Ing. J. H. (Jo) Wallng + CU + CU CU CU (6) + + And for the condton accordng to Eq (): CMCU, + CU + CU CU CU (7) + + The programmng of ths common mode crcut resstance unbalance s defntely more cumbersome and should be mplemented only f there s a real customer demand expected n North Amerca. Agan under maxmum specfed conductor resstance unbalance beween all pars we get CMCU CMCU,, (8) for the condtons accordng to the EQs (0) and (), respectvely. Hence we get two dfferent common mode crcut resstance unbalances, as before, but based upon the Loop resstances of the consdered par combnaton. Note: PoE and PoEP are mplemented by IEEE 80.3af and IEEE 80.3ar respectvely, both beng nternatonal organzatons, and as such followng IEC rules. TIA may follow the ASTM defnton though. The mplementaton of these addtonal calculatons of already mplemented measurements should be done ASAP, n order to assess future cables desgn optons to comply to emergng requrements. Jo Wallng Beaconsfeld, July 4, 006 5 43 Church, Beaconsfeld, QC, H9W 39, Canada (54) 695-80 or (54) 695-6063 Fax: (54) 695-80