The initiation of Rayleigh-Benard type instability of the mechanical equilibrium during the electrolysis of CuSO4 diluted solution with Cu electrodes has been researched for the cell with relatively small "aspect ratio" (radius-to-depth ratio). All the measurements were done at room temperature and at the natural pH of copper solution in the quasi-amperostatic conditions. The instability and disruption of the convective cell at a sufficiently elevated value of concentration gradient is considered. We calculated a series of critical Rayleigh numbers and compared them with the analogous data for thermal convection. The region of stable convective cell occurrence is found for a variety of interelectrode distances.