In degenerate semiconductors, the Lorenz number L has a strong dependency on certain system parameters: dimensionality, strength of interatomic interactions and Fermi level. This law is not valid or the value of the Lorenz number can be reduced at least in the following cases: manipulating electronic density of states, varying doping density and layer thickness in superlattices and materials with correlated carriers. In thermoelectric materials there are also corrections due to boundary conditions, specifically open circuit vs. closed circuit.