In electrical engineering, a disconnector, disconnect switch or isolator switch is a type of switching device with visible contacts, used to ensure that an electrical circuit is completely de-energized for service or maintenance. They are often found in electrical distribution and industrial applications, where machinery must have its source of driving power removed for adjustment or repair. Disconnectors can be operated manually or by a motor, and may be paired with an earthing switch to ground the portion that has been isolated from the system for ensuring the safety of equipment and the personnel working on it.
High-voltage disconnectors are used in electrical substations to allow isolation of apparatus such as circuit breakers, transformers, and transmission lines, for maintenance. The disconnector is usually not intended for normal control of the circuit, but only for safety isolation. Unlike load switches and circuit breakers, disconnectors lack a mechanism for suppression of electric arcs which occur when conductors carrying high currents are mechanically interrupted. Thus, they are off-load devices, with very low breaking capacity, intended to be opened only after the current has been interrupted by some other control device. Safety regulations of the utility must prevent any attempt to open the disconnector while it supplies a circuit. Standards in some countries for safety may require either local motor isolators or lockable handles (which can be padlocked).
IEC standard 62271-102 defines the functionality and features of a disconnector.
Disconnectors have provisions for a 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 disconnector has the additional ability to earth the isolated circuit thereby providing additional safety. Such an arrangement would apply to circuits that inter-connect power distribution systems where both ends of the circuit need to be isolated.
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