Automotive EMC test harnesses: standard lengths and their effect on conducted emissions

The harness used on any vehicle is unique to that model, having a specific length of wiring to optimize connections between circuits and a unique configuration of signal and power cabling for each model. The international automotive EMC standards, however, all specify specific "standard" lengths for test purposes. While using a standard harness length makes comparison of results easier to perform for different electronic-sub assemblies (ESA) for use on vehicles, does it affect the actual test performance? Presented here is the result of radiated emissions tests conducted to the European automotive EMC directive (95/54/EC) utilising five different "standard" length test harnesses and a wide-band noise source. The results illustrate the differences that the harness length has on this individual test technique and discussion on the implications this may have on final installation is provided.