A modular switch apparatus for controlling at least one electric drive includes a mounting rail bus system having a control line and two power supply lines, a power supply device, and a safety relay module that is configured to obtain a first, high level control signal from a DC supply voltage applied to the two power supply lines and to feed the first control signal to the control line via the first bus interface if the emergency stop command device has not been actuated. Furthermore, at least one safety motor starter module is provided, which includes a processing device with an input that can be electrically connected to the control line via a bus interface. The processing device is adapted to evaluate a first, high level control signal as transferred via the control line and to provide control signals for controlling the at least two switch devices.