Abstract: In the grounding project of the power system, copper stranded wire is a key component used to quickly conduct large currents in fault conditions into the ground. Copper stranded wire is made by twisting multiple copper single wires together. The tensile strength of the single wire when stretched directly affects the mechanical properties of the entire stranded wire. Based on the regulations on copper stranded wires for electrical grounding bodies in DL/T 1342, this paper systematically analyzes the sources of uncertainty caused by force value measurement, diameter measurement and repeatability. Based on the result analysis, it is recommended to use a testing machine of grade 0.5 or above during the inspection, and measure the diameters on multiple cross-sections and take the average value. This can make the measurement results more reliable.