Hydrogen will play an important role as an energy storage in the future. For example, the National Hydrogen Strategy of the Federal Ministry of Economics and Climate Protection (BMWK) provides for the expansion of the installation capacity of electrolysis plants for the production of hydrogen from renewable energies in Germany from the current level of approx. 100 MW to 10 GW. With installation capacities of this magnitude, the availability of the electrolysis plants must be ensured by suitable protection concepts. Knowledge of the contribution of the electrolyser to the short circuit current in the event of a fault in an electrolysis plant is an important prerequisite for the design of protection systems for electrolysis plants. The paper presents the current findings on the short circuit current contribution of electrolysers (short-circuit current curve and parameters, relevant influencing variables) and the resulting research questions. The results are based on investigations carried out at the Institute of Energy Technologies (IET 4, Forschungszentrum Jülich) on a 50 kW PEM electrolyser. Furthermore, the test setup used for the experimental investigation of the short-circuit current of the electrolyser and the test specimens used are described.