  The electric field increases toward infinity in the narrow region between
closely adjacent perfect conductors as they approach each other. Much attention
has been devoted to the blow-up estimate, especially in two dimensions, for the
practical relevance to high stress concentration in fiber-reinforced elastic
composites. In this paper, we establish optimal estimates for the electric
field associated with the distance between two spherical conductors in
$n-${dimensional spaces for $n \geq 2$}. {The novelty of these estimates is
that they explicitly describe the dependency of the blow-up rate on the
geometric parameters: the radii of the conductors.}
