A new microprocessor based synchronous switch has been developed at Virginia Tech as an improvement on the customary solid state electronic or mechanical switch. The author designed and built a 16-pole synchronous switch using a 16 bit microprocessor to provide programmable control on both the opening and closing times for each of the 16 poles of the switch. The user can define a sequence of states (short circuit and open circuit) for each of the 16-poles with control on a) The instant of shorting. b) The instant of opening. The above single shot action can be made repetitive by defining a period of repetition. The device is particularly useful in power system projects and has a unique place in repetitive and 'one time' switching in power system models. The switch is totally self-contained and can be operated through a terminal interfaced to an 8086 microprocessor based microcomputer. The microcomputer was developed and is dedicated to this application alone. The use of 8086 microprocessor facilitates realization of a relatively trouble free, noiseless operation. The system design contains a zero-crossing detector circuit which is used to interrupt the microcomputer for synchronisation. The system has buffered output ports which are connected to mercury wetted relays. These relays are controlled for ON and OFF operation by the user through the above system. The smallest short circuit duration of the order of 2 to 3 msecs can be achieved as determined by the mercury wetted relays. The switch can be used for any purpose where it is desired to accurately control switching points (opening, closing or faulting) on any low power AC network. The switch can be quite useful in studying transient phenomena on three-phase system models. The switch is useful in studying responses of various relaying schemes where it is desirable to test the relay at precise switching angles. Additionally, the switch would be very useful to test or operate circuit breaker models in the power simulation laboratory. / M.S.