The interaction between plasma rotation and perturbation fields is described by the ambipolarity constraint and the parallel momentum balance, both emanating from the revisited neoclassical theory, and the electrodynamical screening of the resonant perturbation field at the singular surfaces. This screening depends mainly on the slip between the rotating plasma and the resonant field. The neoclassical theory, valid in the collision dominated regime and accounting for gyro viscosity includes arbitrary plasma cross-sections, anomalous viscosity, ponderomotive forces, Neutral Beam Injection (NBI), pressure anisotropization and a momentum source due to ergodicity which has a considerable impact on the plasma rotation as demonstrated in TEXTOR. To estimate the influence of the perturbation coils on the plasma rotation, the radial magnetic field (proportional to the helical flux function) are Fourier analyzed (using 'intrinsic' coordinates) and the total field is used for field line tracing thus obtaining the ponderomotive momentum input and the extension ∆e of the ergodic layer at the edge. Both procedures account for the full plasma geometry. ∆e is assumed to be independent from the rotational state because of the boundary condition Vt = 0. In a second step the obtained velocity profiles are used to compute the screening at the singular layers and thus the reduction of the island width due to plasma rotation.