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We investigate the properties of relativistic star spheres made of anelectrically charged incompressible fluid, generalizing, thus, theSchwarzschild interior solution. The investigation is carried by integratingnumerically the hydrostatic equilibrium equation, i.e., theTolman-Oppenheimer-Volkoff (TOV) equation, with the hypothesis that the chargedistribution is proportional to the energy density. We match the interior to aReissner-Nordstr\"om exterior, and study some features of these star spheressuch as the total mass $M$, the radius $R$, and the total charge $Q$. We alsodisplay the pressure profile. For star spheres made of a perfect fluid there isthe Buchdahl bound, $R/M\geq 9/4$, a compactness bound found from genericprinciples. For the Schwarzschild interior solution there is also the knowncompactness limit, the interior Schwarzschild limit where the configurationsattain infinite central pressure, given by $R/M=9/4$, yielding an instancewhere the Buchdahl bound is saturated. We study this limit of infinite centralpressure for the electrically charged stars and compare it with theBuchdahl-Andr\'easson bound, a limit that, like the Buchdahl bound for theuncharged case, is obtained by imposing some generic physical conditions oncharged configurations. We show that the electrical interior Schwarzschildlimit of all but two configurations is always below the Buchdahl-Andr\'eassonlimit, i.e., we find that the electrical interior Schwarzschild limit does notgenerically saturate the Buchdahl-Andr\'easson bound. We also find that thequasiblack hole limit, i.e., the extremal most compact limit for chargedincompressible stars, is reached when the matter is highly charged and thestar's central pressure tends to infinity. This is one of the two instanceswhere the Buchdahl-Andr\'easson bound is saturated, the other being theuncharged, interior Schwarzschild solution.

Incompressible relativistic spheres: Electrically charged stars, compactness bounds, and quasiblack hole configurations