We embed $\ECat$ into $\REL{\ECat}$ by associating to $f : X\to Y$ the arrow $\prn{\Idn{X},f} : X \to X\times Y$; this embedding factors through the (obvious) embedding of $\ECat\Sub{p}$ into $\REL{\ECat}$.
We embed $\ECat$ into $\REL{\ECat}$ by associating to $f : X\to Y$ the arrow $\prn{\Idn{X},f} : X \to X\times Y$; this embedding factors through the (obvious) embedding of $\ECat\Sub{p}$ into $\REL{\ECat}$.