[MUSIC] In power systems, a disconnect switches, or disconnectors, are used to ensure that an electric circuit is completely deenergized for service or maintenance. Such switches are often found in electrical distribution and industrial applications. Where machinery must have it's source of driving power removed for adjustment or repair. High voltage switches are used in electrical substations to allow isolation of apparatus, such as the circuit breakers, transformers and transmission lines for maintenance. The switches are usually not intended for normal control of the circuit, but only for safety isolation. They can be operated either manually or automatically. Unlike circuit breakers, disconnect switches lack a mechanism for suppression of electric arcs. Which occur when conductors carrying high currents are electrically interrupted. Thus, they are off-load devices, intended to be opened only after current has been interrupted by some other control device, such as a circuit breaker. Safety regulations of the utility must prevent any attempt to open the disconnect switch while it supplies a circuit. Standards require lockable overloads, which can be padlocked. Disconnect switches have provisions for lockout, tagout, so that inadvertent operation is not possible. In high voltage or complex systems, these locks may be part of a trapped key interlock system to ensure proper sequence of operation. In some designs, the disconnect switch has the additional ability to ground the isolated circuit, thereby, providing additional safety. They are called grounding switches. Such an arrangement would apply to circuits with interconnect power distribution systems, where both ends of the circuit need to be isolated. Circuit breakers and disconnect switches are equally capable of preventing the return of power, once they are opened and properly logged and tagged. The real difference is that a circuit breaker can trip open when it detects an overcurrent situation. Disconnect switches are usually installed on both sides of the equipment or line upon which work is to be done. They should not be operated while the circuit in which they are connected is energized. But only after the circuit is deenergized. As a further precaution, they may be opened by means of an insulated stick that helps the operator keep a distance from the switch. Although, not designed to be closed to energize the line or equipment with which they are associated. In certain circumstances, they may be closed using special care to close them firmly and rapidly. High voltage switches are available for the highest transmission voltages up to 1 million volts. This switch is operated, so that all three phases are interrupted at the same time.