IEC 61788-4:2016 specifies a test method for the determination of the residual resistance ratio (RRR) of Nb-Ti and Nb₃Sn composite superconductors with Cu, Cu-Ni, Cu/Cu-Ni and Al matrix. This method is intended for use with superconductor specimens that have a monolithic structure with rectangular or round cross-section, RRR value less than 350, and cross-sectional area less than 3 mm². In the case of Nb₃Sn, the specimens have received a reaction heat-treatment. This fourth edition cancels and replaces the third edition published in 2011. This edition constitutes a technical revision.