\documentclass{standalone}

\usepackage{tikz,pgfplots}
\usepackage{siunitx}
\usepackage[siunitx,european]{circuitikz}
\usepackage{mathrsfs}
\usetikzlibrary{arrows}
\usepackage{amsbsy}
\usetikzlibrary{fadings}
\usetikzlibrary{patterns}
\usetikzlibrary{automata,positioning}
\usepackage{mwe,subcaption,tikz}
\tikzset{boximg/.style={remember picture,red,thick,draw,inner sep=0pt,outer sep=0pt}}
\pgfplotsset{compat=1.11}
\begin{document}
\definecolor{mygreen}{rgb}{0,0.78,0}
\begin{tikzpicture}

	\draw (0,0) node[ground]{} to [american current source, l=$P_{D/T}$, v=$\vartheta_j$] (0,2)
	to [short] (0.5,2)
	to [R] (2.5,2)
	to [R] (4.5,2)
	to [short] (5,2)
	to [dcvsource, a=$\vartheta_a$] (5,0) node[ground]{};
	\draw (1.5,2.15) node[above]{$R^{th}_{D/T,j-c}$}
	(3.5,2.15) node[above]{$R^{th}_{D/T,c-a}$};
\end{tikzpicture}
\end{document}