c-Axis current flow arises in helically wound wire

c-Axis critical current density of second-generation YBCO wires in HTS cables due to the interaction of current flow with the induced magnetic field. However, the importance of c-axis critical current density ($J_{c}^{c})$ on the overall transport critical current is not clearly understood. We measured the temperature and field dependence of $J_{c}^{c}$ using a mesa structure patterned into the YBCO layer of 2$^{nd}$-generation HTS tapes. We found, $J_{c}^{c}$ --values of $\sim $ 4 kA/cm$^{2}$ at 77 K in self-field, corresponding to an unexpectedly high anisotropy of the critical current density $\gamma ={J_c^{ab} } \mathord{\left/ {\vphantom {{J_c^{ab} } {J_c^c }}} \right. \kern-\nulldelimiterspace} {J_c^c }=$ 500$\sim $600. We also investigated the effect of pinning microstructures on $J_{c}^{c}$ and $\gamma $. Our result shows a direct correlation of $J_{c}^{c}$ (77 K, sf) and $\gamma $ to the density of stacking faults. An estimation reveals that the fraction of tape width associated with $c$-axis current flow grows linearly from 5{\%} to 20{\%} with increasing $\gamma $ for a typical geometry and could affect the performance of power transmission in HTS cables.