Normal electrolysis at high voltages switches over spontaneously to contact glow discharge electrolysis. The transition is profoundly facilitated by raising the temperature and/or lowering the surface tension of the electrolyte. Results of a systematic study on the influence of these two factors on the breakdown voltage for normal electrolysis have been critically analysed. It has been concluded that solvent vaporisation near an electrode by Joule heating during electrolysis and the onset of hydrodynamic instabilities in local solvent vaporisation are the prime causes for the breakdown of normal electrolysis.