Part of a membrane-bound complex that couples electron transfer with translocation of ions across the membrane. Couples electron transfer from reduced ferredoxin to NAD(+) with electrogenic movement of Na(+) out of the cell. Involved in caffeate respiration. H(+) + Na(+)(in) + NAD(+) + 2 reduced [2Fe-2S]-[ferredoxin] = Na(+)(out) + NADH + 2 oxidized [2Fe-2S]-[ferredoxin] Binds 7 [4Fe-4S] clusters. The complex is composed of six subunits: RnfA, RnfB, RnfC, RnfD, RnfE and RnfG. Belongs to the 4Fe4S bacterial-type ferredoxin family. RnfB subfamily.