In this paper, a method to solve magnetostatic problems for non-conforming meshes using penalty method is presented, where the interface conditions are imposed at the integration points. In the case of non-conforming meshes, there are two interfaces at the contact of the two bodies, so in order to impose the interface conditions, which connect the two bodies involved, the interface conditions must be expressed with respect to one interface, in this case I call slave, the body containing this interface and the other the master one. The best choice of the slave body, in order to obtain the most accurate solution, is investigated in this paper. Furthermore, this paper introduces a novel formulation known as the bi-pass or symmetric formulation, where each body is taken simultaneously as slave and as master, so there is no need to make the best choice of the slave body which in some situations is difficult to do. Additionally, this formulation leads to more accurate solutions