The power management control system comprises a computer having standard RS485 interface cards and adapters installed in its I/O slots defining multiple industry standard Modbus RTU networks. The computer contains software for monitoring and controlling selected aspects of power usage/consumption, as described in more detail hereinafter. The Modbus RTU protocol is a well known industry standard. Devices with a Modbus RTU interface can be connected directly to the Modbus and other devices which communicate on the Commnet protocol require a Modbus concentrator. The Modbus concentrator provides an interface between the Modbus RTU protocol and the Commnet protocol, whereby these other devices can communicate through the Modbus concentrator over the Modbus. Alternatively, standard Ethernet interface cards and adapters are installed in the computer's I/O slots defining multiple standard Ethernet TCP/IP networks. The Ethernet TCP/IP protocol is a well known standard, which would allow a user of the power management control system of the present invention to use its existing LAN. Ethernet gateways are connected to the Ethernet TCP/IP networks to provide an interface between the Ethernet TCP/IP protocol and the Modbus RTU protocol.