Abstract: An electric transfer switch unit for selective connection to different power supplies is provided with moveable contacts, associated stationary contacts connected to said power supplies, a turnable drive handle and a toggle mechanism for connecting the drive handle to the moveable contacts. The toggle mechanism includes a spring system adapted for storing and releasing mechanical energy upon turning of the drive handle. Use of the spring system assures swift and stable turning of the drive handle for shifting between the different power supplies.

Abstract: An electric transfer switch unit for selective connection to different power supplies is provided with moveable contacts, associated stationary contacts connected to said power supplies, a turnable drive handle and a toggle mechanism for connecting the drive handle to the moveable contacts. The toggle mechanism includes a spring system adapted for storing and releasing mechanical energy upon turning of the drive handle. Use of the spring system assures swift and stable turning of the drive handle for shifting between the different power supplies.

Abstract: A change-over switch performs switching between two different power supplies after connecting both power supplies simultaneously for a given time period. A controller controls the change-over switch to perform the switching operation around a synchronous point of the power supplies. Voltages of the power supplies are monitored to derive a difference voltage therebetween. From the difference voltage, a phase difference between the voltages of the power supplies is monitored. A plurality of low voltage detectors are provided for monitoring the difference voltage. The low voltage detectors are arranged to be operated at voltage values no more than preset values, respectively. The controller outputs a switching command to the change-over switch when time intervals between adjacent operation start time points of the low voltage detectors are all greater than preset values, respectively, and when the low voltage detectors are all operated.

Abstract: In construction of a switching device interposed between a pair of power sources and a load circuit and provided with switch and by-pass units, the switch unit is extractable from its housing and operation of the by-pass circuit is interlocked with position of the switch unit with respect to the housing so that the load circuit should be selectively connected to one of the two power sources. For convenience in maintenance and/or operation of device elements, shift of connection of the load circuit from one to the other power source can be performed by an interlocked operation of the two units without any contact damage and incorrect power source connection.