How can I increase the size of the open pole ocirc
without affecting other components?
There is \ctikzset{nodes width=0.15}
in the manual but this would also increase the size of ocirc in the switch.
\documentclass[tikz, border=1cm]{standalone}
\usepackage[american, siunitx]{circuitikz}
\begin{document}
\begin{tikzpicture}[thick]
\ctikzset{nodes width=0.15}
\draw (0,5) node[ocirc] at (0,5){} to [I] ++ (2,0) to [cute closing switch] ++(2,0);
\end{tikzpicture}
\end{document}