Frequency-dependent electrical conductivities of solutions of aqueous sodium chloride have been measured from T = 298 K to T = 623 K at p = 20 MPa, over a very wide range of ionic strength (2.10(-5) to 0.17 mol.kg(-1)) using a unique high-precision flow-through alternating current (AC) electrical conductance instrument. Experimental values for the equivalent conductivity, Lambda, were used to calculate molar conductivities at infinite dilution, Lambda degrees, using the Fuoss-Hsia-Fernandez-Prini (FHFP) and Turq-Blum-Bernard-Kunz (TBBK) ionic conductivity models. The resulting values for the limiting conductivity Lambda degrees and the ion association constant of NaCl, from this work and critically evaluated literature data above 277 K, were represented to within the combined experimental uncertainties, as functions of viscosity and solvent density, respectively. New values and new correlations are reported for the limiting equivalent conductivities of the sodium ion, lambda degrees(Na+), and the chloride ion, lambda degrees(Cl-) from 277 K and 100 kPa to 1073 K and 500 MPa.