Two parallel wires attract if the relative sense of the currents is in the same direction.  This animation shows that this attraction can be understood as due to the tension in the magnetic field pulling the two wires together.
<a rel="nofollow" class="external text" href="https://www.youtube.com/user/ElectromagnetismAnim">John Belcher</a>
CC BY 3.0
<bdo lang="en" dir="ltr"><a href="//commons.wikimedia.org/wiki/Commons:YouTube_files" title="Commons:YouTube files">YouTube</a>: <a rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=nQX-BM3GCv4"><bdi lang="">Parallel Wires 640</bdi></a> – View/save archived versions on <a rel="nofollow" class="external text" href="https://web.archive.org/web/*/https://www.youtube.com/watch?v=nQX-BM3GCv4">archive.org</a> and <a rel="nofollow" class="external text" href="https://archive.today/https://www.youtube.com/watch?v=nQX-BM3GCv4">archive.today</a></bdo>