\documentclass[tikz,convert=false]{standalone}
\usetikzlibrary{calc}
\tikzset{double -|/.style={to path={%
($(\tikztostart)+(0,3pt)$) -| ($(\tikztotarget)+(-3pt,0)$)
($(\tikztostart)+(0,-3pt)$) -| ($(\tikztotarget)+(3pt,0)$)
}}}
\begin{document}
\begin{tikzpicture}[nodes={circle,draw}]
\node (a) {$a$};
\node (c) at (2,1) {$c$};
\draw (a.east) to[double -|] (c.south);
\end{tikzpicture}
\end{document}