Page 54 - 4587

withstand voltage is assured between the open contacts of the main
circuit of the switchgear.
It must also be equipped with an indicator device in relation to
the position of the movable contacts. This position indicator must
be linked in a secure, reliable way to the actuator, whereby the
position indicator can also serve as actuator, provided that it can
only display the position “Open” in the “OFF” position, when all
moving contacts are in the “Open” position. This is to be verified
by testing.
According to IEC 60947-3, an isolator must only be able to
make and break a circuit, if either a current of negligible size is
switched on or off, or if during switching no noticeable voltage
difference between the terminals of each pole occurs.
Under normal conditions it can conduct operational currents as
well as under abnormal conditions larger currents (e.g. short-
circuit currents) for a certain period.
The isolator function can be realized with a variety of devices
such as for example in disconnectors, fuse-disconnectors, switch-
disconnectors, fuse-switch disconnectors and circuit breakers with
isolating function.

2. Load switches

Load switches (or only “switches”) are mechanical switching
devices capable of making, carrying and breaking currents under
normal circuit conditions which may include specified operating
overload conditions and also carrying for a specified time currents
under specified abnormal circuit conditions such as those of short-
circuit.
A load switch may have a short-circuit making capacity,
however it does not have a short-circuit breaking capacity (IEC
60947-1 and -3).
Short-circuit currents can be conducted (high short-circuit
withstand capacity), but not be switched-off.
For load switches the range of designs is similarly wide as for
isolator switches, for example “normal” (load) switches, fuse-
switches, circuit breakers.
Fuse-switches are not legally permitted in all countries.

53