An R&D program at CRPP investigates the design of large size Nb3Sn conductors, with the aim to improve the effectiveness and hence the cost of large size, force flow conductors. A design based on a solder filled flat cable, by react wind method, is selected for a demonstration prototype, built at CRPP and tested in the SULTAN facility. In the new conductor, the longitudinal strain is similar to the strand intrinsic strain because the cable is heat treated without steel jacket. The transverse load degradation is suppressed thank to effective mechanical support of the strands by the solder matrix. The test in SULTAN includes dc test, ac loss in superimposed dc and ac field and transient field stability. At 48 kA (430 A/mm(2)) and 11.15 T the current sharing temperature is 6.3 K, i.e. the new conductor provides a higher temperature margin and saves about 50% of the Nb3Sn cross section, in comparison to ITER. The transient stability largely fulfils the ITER requirement.