A SCADA communication and control system is used for controlling power distribution. The system includes a master controller, a master ratio and a plurality of remote terminal units (RTUs). A communication link between the master controller and the master radio has two channels. A first channel is for sending master controller messages to the master radio. The second channel is for the master radio to send the RTU response messages back to the master controller. A supplemental controller along with supplemental remote terminal units (SRTUs) also are included for expanding the range of the system. A switch is included in the second channel so as to selectively link either the supplemental controller or the master radio to the master controller for providing response messages. The supplemental controller monitors the first channel to identify messages having an SRTU address. When such a message is identified, the switch is set to select the supplemental controller. In addition, the master radio is disabled from transmitting over the 900 MHz radio channel. Thus for SRTU communications, the supplemental controller has access to the 900 MHz channel and the response link back to the master controller. The supplemental controller includes a main task for monitoring and testing master controller messages. The main task defines the switch state and enables/disables the master radio access to the 900 Mhz channel. A network task also is included which controls communications with the SRTUs, either directly or through a sub-controller.