\begin{figure}[h]
    \begin{circuitikz}[american voltages]
        \draw
        (4,-1) to[short] (4,-2)
        (5,-1) to[short] (5,-2);
        \draw (4,-2) to[open,v_>=$U_S$] (5,-2);
    \end{circuitikz}
\end{figure}