In electrical engineering, a disconnector or isolator switch is
used to make sure that an electrical circuit can be completely
de-energised for service or maintenance. Such switches are often
found in electrical distribution and industrial applications
where machinery must have its source of driving power removed for
adjustment or repair. High-voltage isolation switches are used in
electrical substations to allow isolation of apparatus such as
circuit breakers and transformers, and transmission lines, for
maintenance. Often the isolation switch is not intended for
normal control of the circuit and is used only for isolation; in
such a case, it functions as a second, usually physically distant
master switch (wired in series with the primary one) that can
independently disable the circuit even if the master switch used
in everyday operation is turned on.
Isolator switches have provisions for a padlock so that
inadvertent operation is not possible (see: Lockout-Tagout). In
high voltage or complex systems, these padlocks may be part of a
trapped-key interlock system to ensure proper sequence of
operation. In some designs the isolator switch has the additional
ability to earth the isolated circuit thereby providing
additional safety. Such an arrangement would apply to circuits
which inter-connect power distribution systems where both end of
the circuit need to be isolated.
