\documentclass{standalone}
\usepackage[american]{circuitikz}
\usepackage{graphicx}
\usepackage{mathrsfs} 
\usepackage{latexsym,amssymb,amsmath}

\newcommand{\equal}{=}
\begin{document}
	\begin{circuitikz}
		\draw (0,3) to [V,l_=$\mathscr{F}\equal NI$] (0,0) 	% "Voltage source for magentic circuit"
		(0,3) to [R,l^=$\mathscr{R}_{1,thick}$, v_>=$\mathscr{F}_1$, color=red] (0,6)	%Reluctance thick side
		(0,6) to [R, l^=$\mathscr{R}_{2,thin}$,v_>=$\mathscr{F}_2$, color=blue] (3,6)   %Reluctance thin side
		(3,6) -- (3,3)		% Connection R2, R3
	    (3,3) to [R, l^=$\mathscr{R}_{3,thick}$,v_>=$\mathscr{F}_3$, color=red] (3,0)   %Reluctance thick side
	     (3,0) to [R, l^= $\mathscr{R}_{4,thin}$,v_>=$\mathscr{F}_4$, color=blue] (0,0); %Reluctance thin side
	     
	    \draw[thin, <-, >=triangle 45] (1.5,3) node[scale=2]{$\phi$}  ++(-90:1) arc (-90:100:1);
		\end{circuitikz}
	\label{fig:q1fig}
\end{document}