IEC 61788-11:2011 covers a test method for the determination of the residual resistance ratio (RRR) of Nb3Sn composite superconductors. This method is intended for use with superconductor specimens that have a monolithic structure with rectangular or round cross-section, RRR less than 350 and cross-sectional area less than 3 mm2, and have received a reaction heat-treatment. Ideally, it is intended that the specimens be as straight as possible; however, this is not always the case, thus care must be taken to measure the specimen in its as received condition. All measurements are done without an applied magnetic field. The method described in the body of this standard is the "reference" method and optional acquisition methods are outlined in Clause A.3. This second edition cancels and replaces the first edition published in 2003. It constitutes a technical revision. The main revisions are the addition of two new annexes, "Uncertainty considerations" (Annex B) and "Uncertainty evaluation in test method of RRR for Nb3Sn" (Annex C).