Simple formulas were derived to quickly estimate maximum crosstalk between wires in a harness at high frequencies, where the length of circuits is comparable with or greater than the wavelength of the signals of interest. Formulas were derived from multi-conductor transmission line theory. When the source and load resistances are either both large or both small compared to the characteristic impedance of the transmission line, maximum coupling is shown to be given by approximately XMAX = Cm / (C22 + Cm). A similar equation was found for the case where the load impedances are matched. Experiments show these equations predict the maximum value of coupling well
