Abstract: An electrical power control system is adapted for controlling power and lighting in a building. Switch controls have either relays or triacs, controlled by microprocessors, to switch power on electrical branch circuits. An interface device 122 communicates with the switches 124,126, arranged in a multidrop configuration, with variable length data packets over serial branch circuits or data buses 142. In addition to being controlled by the interface device 122, the switch controls also have local switch actuators. The actuation of the local switch controls can be used by the interface device 122 as a control inputs to initiate other actions. Adaptive polling of switch controls is used to minimize system response time, and both transmit and receive signals are carried between the switch controls and the interface device 122 at different times on the same twisted pair wires. The interface device 122 can also communicate with a home automation system controller.