An important operational aspect of modern grids is implementation of a continuous assessment of low-order harmonic emissions from customer installations. While this problem was previously considered in MV systems by the same authors, this paper focuses on the interface between the HV grid and MV distribution systems. The voltage harmonic vector (VHV) approach is utilized to interpret quantities measured at the point of common coupling (PCC), either to check specific assigned emission limits, or to assess customers’ installations contributions to the total harmonic distortion. An HV/MV test system is proposed, combining the HV test system previously proposed by CIGRE/CIRED JWG C4/B4.3S with the MV IEEE benchmark test system previously proposed by the IEEE PES TF on “Harmonic Modeling, Simulation and Assessment”. The analysis is conducted by means of iterative harmonic analysis, in order to manage large number of MV-HV components, as well as to deal with the resonances. The presented results illustrate differences when actual and reference impedances of HV system and MV customer installations are used for the analysis, confirming the overall good performance of the VHV approach when applied at the interface between HV and MV systems.