There are two ways to calculate this kind of fault:

• Use a 4-wire model in which the N-conductor is explicitly modelled and the PE-wire is reduced and modelled as earth. Then when a phase to ground Short-Circuit is calculated, the phase to PE-wire is reproduced.
• The second option is to use a model with the PE-wire explicitly modelled, as an additional single-phase model. For this approximation it is necessary to add an auxiliary node for IEC/VDE SC calculation.

In the attached example note that the result for both approximations is the same.