  We investigate the properties of relativistic star spheres made of an
electrically charged incompressible fluid, generalizing, thus, the
Schwarzschild interior solution. The investigation is carried by integrating
numerically the hydrostatic equilibrium equation, i.e., the
Tolman-Oppenheimer-Volkoff (TOV) equation, with the hypothesis that the charge
distribution is proportional to the energy density. We match the interior to a
Reissner-Nordstr\"om exterior, and study some features of these star spheres
such as the total mass $M$, the radius $R$, and the total charge $Q$. We also
display the pressure profile. For star spheres made of a perfect fluid there is
the Buchdahl bound, $R/M\geq 9/4$, a compactness bound found from generic
principles. For the Schwarzschild interior solution there is also the known
compactness limit, the interior Schwarzschild limit where the configurations
attain infinite central pressure, given by $R/M=9/4$, yielding an instance
where the Buchdahl bound is saturated. We study this limit of infinite central
pressure for the electrically charged stars and compare it with the
Buchdahl-Andr\'easson bound, a limit that, like the Buchdahl bound for the
uncharged case, is obtained by imposing some generic physical conditions on
charged configurations. We show that the electrical interior Schwarzschild
limit of all but two configurations is always below the Buchdahl-Andr\'easson
limit, i.e., we find that the electrical interior Schwarzschild limit does not
generically saturate the Buchdahl-Andr\'easson bound. We also find that the
quasiblack hole limit, i.e., the extremal most compact limit for charged
incompressible stars, is reached when the matter is highly charged and the
star's central pressure tends to infinity. This is one of the two instances
where the Buchdahl-Andr\'easson bound is saturated, the other being the
uncharged, interior Schwarzschild solution.
