  This paper proves results about the Jacobians of a certain family of covering
graphs, $Y$, of a base graph $X$, that is constructed from an assignment of
elements from a group $G$ to the edges of $X$ ($G$ is called the voltage group
and $Y$ is called the derived graph). Of particular interest is when the
voltage assignment is given by mapping a generator of the cyclic group of order
$d$ to a single edge of $X$ (all other edges are assigned the identity), called
a single voltage assignment. Both the order and abelian group structure of the
Jacobian of single voltage assignment derived graphs are determined when the
base graph $X$ is the complete graph on $n$ vertices, for every $n$ and $d$.
Using zeta-functions, general product formulas that relate the order of the
Jacobian of $Y$ to that of $X$ are developed; these formulas become very simple
and explicit in the special case of single voltage covers of $X$.
