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The toroidal field coils and the central solenoid of ITER are to be wound from Nb3Sn CICC (cable-in-conduit conductors) which can be operated up to 68 kA, 11.8 T and 41.4 kA, 13.5 T respectively. The design approach of these conductors is based on the optimization of both the cable current density and the quantity of sc (superconducting) strand in the cable for the most severe conditions expected during operation. The amount of sc strands and the total amount of copper in cables are set by design rules such as "temperature margin" to operate below the critical current, "Stekly parameter" to ensure stability in operation and "hot spot temperature" in case of quench. The design approach is reviewed on the basis of the test results of the ITER Model Coils conductors. A sensitivity study is then carried out to assess the impact on the conductor design of parameters such as the strand critical current density (Jc), the residual resistivity ratio of copper (RRR), the copper to noncopper ratio of the sc strands as well as some of the operating conditions.