Self-field ac losses were measured by the conventional ac four-probe method in biaxially aligned Y–Ba–Cu–O tapes using polycrystalline Hastelloy tapes with textured yttria-stabilized-zirconia buffer layers. The ac losses increased in proportion to the fourth power of transport current in the highJcsample, and agreed well with Norris’ equation for thin strip conductors. However, the lowJcsample had rather higher losses than Norris’ prediction, suggesting excessive magnetic flux penetration caused by percolated current paths. The results confirmed Norris’ prediction of the low ac losses for thin strip conductors, and indicated the importance of removing percolated structures of current paths to avoid higher ac losses than the theoretical predictions based on uniform conductors. ©1997 American Institute of Physics.