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A newly built pharmaceutical plant has been investigated by measurements. Currents of 0.3 kA were injected in the lightning protection grid on the roof. Inside the building, test cables of 100 m length followed a path typical for cables belonging to the installation. We measured induced cable currents and voltages. A reduced model of the building incorporated most of the designed current paths. Measurements and model showed that the roof steel skeleton carried about 80% of the current and the intended lightning conductors 20%. The calculated current through a cable support was larger than measured. This is explained by also considering a nearby nonintended conductor. For three types of cables, we determined the transfer impedances. The measurements and model have been combined and extrapolated to actual lightning.