Q: Circuitikz: How can I specify the direction of rotation for a label? The following MWE rotates the label by +90°. How can I achieve rotation by -90° without changing the direction of the drawn path?
MWE:
\documentclass[margin=5mm]{standalone}
\usepackage{amsmath}
\usepackage{siunitx}
\usepackage{tikz}
\usepackage[european, straightvoltages,americanvoltages]{circuitikz}
\begin{document}
\begin{circuitikz}
\draw (0,0) to[R,l={\mbox{$R=\SI{50}{\ohm}$}},label/align=rotate] (0,-2);
\end{circuitikz}
\end{document}


A: Using just circuitikz, you can't; label directions are fixed, and try to follow the stroke direction when using rotate, in the same way the sloped TikZ option work. But you can (being careful about the rotation center, and about protecting the [align=c] from the TikZ parser), do this:
\documentclass[margin=5mm]{standalone}
\usepackage{amsmath}
\usepackage{siunitx} % siunitx option to circuitikz will load it, also
%\usepackage{tikz}% circuitikz will load it
\usepackage[european, americanvoltages]{circuitikz}
\begin{document}
\begin{circuitikz}
    \ctikzset{label/align=rotate}
    \draw (0,0) to[R,l={\rotatebox[origin=c]{180}{$R=\SI{50}{\ohm}$}}] (0,-2);
    \draw[red] (2,0) to[R,l={$R=\SI{50}{\ohm}$}] (2,-2);
\end{circuitikz}
\end{document}


I have also removed the (confusing, and useless) straightvoltages, which is overridden by americanvoltages.
