Abstract: A system for transferring a load from a first to a second AC power source, including a monitor for sensing both power sources and producing an output signal when the differences in voltage, frequency, and phase between the two sources are within prescribed limits. Contacts close, in response to the monitor output signal, to connect the second power source to both the first power source and the load. Other contacts open, to disconnect the first power source from the second power source and load, but only after the second power source has been connected to the first power source and the load. The contact arrangement may include an automatic transfer switch and separate contacts in parallel with one or both sets of transfer switch contacts, or it may involve two independently operable contactors, or it may involve a four position switch.

Abstract: A control panel, formed entirely of solid state components, for an automatic transfer switch which alternatively connects a load to a normal source of power or starts up an emergency source of power and connects the load to it. The control panel includes monitors for the normal and emergency sources, the monitors having a pickup voltage and a lower dropout voltage, relays for initiating operation of the emergency or normal sources when the normal source drops below the dropout level or the emergency source rises above the pickup voltage or frequency level, and time delay circuits between the monitors and the relays preventing operation of the relays unless the voltage levels exist beyond the time periods provided.

Abstract: An automatic transfer switch having two sets of phase switches, one set for connection between a normal power source and a load and the other set for connection between an emergency power source and the load. The transfer switch also includes two neutral switches, one for connection between the normal source neutral and the load neutral, and the other for connection between the emergency source neutral and the load neutral. Only one set of the phase switches can be closed at any one time, and during transfer of the load from one source to the other both sets of phase switches are open. Prior to a transfer operation, the neutral switch corresponding to the closed set of phase switches is closed and the neutral switch corresponding to the open set of phase switches is open. During transfer of the load, both neutral switches are closed before the closed set of phase switches open and both neutral switches remain closed until after the closed set of phase switches open and the open set of phase switches close.

Abstract: An automatic transfer switch having two sets of phase switches, one set for connection between a normal power source and a load and the other set for connection between an emergency power source and the load. The transfer switch also includes two neutral switches, one for connection between the normal source neutral and the load neutral, and the other for connection between the emergency source neutral and the load neutral. Only one set of the phase switches can be closed at any one time, and during transfer of the load from one source to the other both sets of phase switches are open. Prior to a transfer operation, the neutral switch corresponding to the closed set of phase switches is closed and the neutral switch corresponding to the open set of phase switches is open. During transfer of the load, both neutral switches are closed before the closed set of phase switches open and both neutral switches remain closed until after the closed set of phase switches open and the open set of phase switches close.