\documentclass{standalone}

%%\usepackage{tikz}
\usepackage[european]{circuitikz}

\begin{document}

\begin{circuitikz}
    \draw (0,0) to [vsource, V=$U_0$] (0,6) to [short, -*, i=$I_0$] (2,6)
    to [R=$R_1$] (2,3) to [R=$R_6$] (2,0);
    \draw (2,6) to [short, -*] (4,6) to [R=$R_2$] (4,3) to [R=$R_7$] (4,0);
    \draw (4,6) node[above]{$K_1$} to [short, -*] (8,6) to [R=$R_3$] (8,3) to [R=$R_8$] (8,0);
    \draw (8,6) to [short, -*] (10,6) to [R=$R_4$] (10,3) to [R=$R_9$] (10,0);
    \draw (2,3) node[left]{$K_2$} to [short, *-*] (4,3) to [R=$R_5$] (8,3) to
    [short, *-*] (10,3) node[right]{$K_3$};
    \draw (10,0) to [short, *-*] (8,0) to [short, -*] (4,0) to [short, -*] (2,0)
    to [short] (0,0);
    \draw (2,0) node[ground]{} (2,-1);
\end{circuitikz}


\end{document}