A layered system of external currents is used to model the electric environment of a mesoscale convective system (MCS). The model takes into account the multilayer structure and appropriate horizontal scales of the MCS charge regions. The detailed model determines the electric field and current inside and in the vicinity of a stationary MCS as well as the net vertical current above the thunderclouds, which is an important measure of its contribution to the global electric circuit. The relatively large horizontal scale of an MCS ensures a more effective coupling to the ionosphere than for an isolated thunderstorm. In the model calculations the MCS-trailing stratiform region had a net vertical current magnitude of about 25 A versus only 0.4 A for a convective element of the MCS (which is similar to the contribution of an isolated thunderstorm). Additionally, it has been found that an MCS can serve either as an effective generator in the global circuit or as a discharger of it depending on the polarity, magnitude, and thickness of the layers of external current.