In OM2p and OM3p geometries, the default external boundary condition is PEC, as listed in “Default Boundary Conditions”. Any external geometry boundary is treated with the PEC boundary condition, unless otherwise specified. In simulations with natural symmetry, you may use symmetry boundary conditions to dramatically reduce the computational burden of your simulation. There are two types of symmetry planes: electric and magnetic. An electric symmetry plane is appropriate when the electric field is symmetric across the plane. Physically, the electric symmetry plane is equivalent to a perfect magnetic conductor (PMC) boundary, so there can be no normal component to the H field, and symmetry is enforced in the E field. A magnetic symmetry plane is appropriate when the magnetic field is symmetric across the plane. The magnetic symmetry plane is physically equivalent to a PEC boundary, so there can be no normal component to the E field on the boundary, and symmetry is enforced in the H field.