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 currents. Unlike oil switches, vacuum switches require virtually no maintenance. They can be
used for submersible or padmount operation.
3.4.4 Switch Accessories. Switch accessories are devices that perform a secondary or minor
duty as an adjunct or refinement to the primary operation of a switch or to assist in the operation
of a switch. Some accessories that are commonly associated with switches are as follows:
3.4.4.1 Operating Mechanisms. The operating mechanism of a switch is a power-operated
interphase connecting rods by which the contacts of all poles are actuated simultaneously.
3.4.4.2 Hook Sticks. A hook stick is a hook provided with an insulating handle (usually
specially treated wood) for opening and closing hook-stick-operated switches. When not being
used, hook sticks should be stored in a dry location.
3.4.4.3 Interlocks. An interlock is a device applied to two or more movable parts,
preventing or allowing a movement of one part only when one or more other parts are locked in a
predetermined position. An interlock system is a series of these devices applied to equipment to
allow operation of the equipment only in a prearranged sequence. Switches used only for
isolating purposes must be interlocked to prevent opening of the isolating switch under load, or
the switch must be provided with a highly visible sign warning against opening the switch under
load. Interlocks are classified into three main divisions: mechanical interlocks, electrical
interlocks, and key interlocks.
3.4.4.4 Auxiliary Switches. Auxiliary switches are low-voltage switches that are attached
to the operating mechanism of gang-operated switches. The open or closed position of auxiliary
switches is governed by the position of the main contacts. Auxiliary switches are used for
electrical interlocking, remote position indication, or control of electrically operated switches.
3.4.5 Operation. Disconnect switches, grounding switches, and air-break switches have no
interrupting rating. It is, however, common practice to use air-break switches to interrupt small
values of current and to use the following general rules.
3.4.5.1 Operation Rules.
(a) Prior to operating, check the circuit to see that no load is being carried by the
switch. If the disconnect switch is installed in series with a circuit breaker or automatic circuit
recloser, inspect the position of the series device to be sure that it is open before operating the
disconnect switch. The indicating lamp or targets on the switchboard should not be relied upon
for positive indication that a circuit breaker is open.
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