The present disclosure proposes: a distributor measuring box designed to be installed on a photovoltaic solar module, having a housing with a support section embodied to be supported on the solar module, an encompassing side wall, and a cover, and string line feedthroughs and/or string line connectors, and having a string current measuring module that includes a measuring component and an evaluation unit for measuring the string current in the distributor measuring box; a photovoltaic solar module having a plurality of solar cells, in which a distributor measuring box is mounted to the back of the solar module oriented away from the sun; and a photovoltaic system having a plurality of photovoltaic solar modules, having a plurality of string lines, having a generator junction box, and having at least one inverter for supplying the electrical power produced by the photovoltaic generator.