[en] Inelastic neutron scattering experiments were performed on (Pr_1.5Ce_0.5)Sr₂Cu₂NbO_10-δ to determine the magnetic ground state of the Pr ions. In this compound, superconductivity is suppressed by the presence of Pr ions. The magnetic ground state is found to be very similar to that in PrBa₂Cu₃O_x and Pb₂Sr₂PrCu₃O₈. However, the high energy spectrum has a stronger resemblance to that of Pr_2-xCe_xCuO₄, where the Pr ions see a very similar local structure. Therefore, a similar set of higher order crystalline-electric-field parameters and an inversion of B₀² can explain qualitatively the neutron spectra. The suppression of superconductivity and the quasi-triplet magnetic ground state support models which correlate the unusual magnetic properties with T_c suppression by Pr. (author)