Abstract: An electric load controller having a modular construction with the logic circuitry located in an enclosure. This circuitry comprises a microprocessor, I/O interface and a memory for storing the computer program to be executed by the microprocessor. The control logic supplies signals via the I/O interface to a set of three modules which switch the three phase electric current to the load. The switch modules each having a separate enclosure containing thyristors which apply the electricity to the load in response to control logic signals. The switch modules are mounted on a heat sink and the logic circuit enclosure is mounted on the switch modules. A protection circuit module may be included that provides a metal oxide varistor and a capacitor connected across each phase of the electric power.