Lipoamide dehydrogenase is a component of the alpha-ketoacid dehydrogenase complexes. Catalyzes the reoxidation of dihydrolipoyl groups which are covalently attached to the lipoate acyltransferase components (E2) of the complexes (By similarity). (R)-N(6)-dihydrolipoyl-L-lysyl-[protein] + NAD(+) = (R)-N(6)-lipoyl-L-lysyl-[protein] + H(+) + NADH Binds 1 FAD per subunit. Homodimer. Part of the PDH complex, consisting of multiple copies of AceE (E1), DlaT (E2) and Lpd (E3), and of the BCKADH complex, consisting of multiple copies of BkdA/BkdB (E1), BkdC (E2) and Lpd (E3). The active site is a redox-active disulfide bond. Belongs to the class-I pyridine nucleotide-disulfide oxidoreductase family.