Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 31)

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.
Disconnector (Load-) Switch Switch-disconnector Circuit breakers
Fig. 2.2-2
Switch symbols
The horizontal line in the switch symbol of the contacts indicates that they fulfill the isolating function
The isolator function can be realized with a variety of devices such as for example in disconnec-
tors, fuse-disconnectors, switch-disconnectors, fuse-switch disconnectors and circuit breakers
with isolating function.
2.2.1.2 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.
2.2.1.3 Switch disconnectors
Switch disconnectors combine the properties of (load) switches and disconnectors.
In this case, too, there are a variety of designs such as “normal” switch disconnectors, fuse-
switch-disconnectors and circuit breakers. Fuse-switch-disconnectors are not legally permitted
in all countries.
2.2.1.4 Circuit breakers
See also Section 4.2.2 . Circuit breakers are mechanical switching devices, capable of making,
carrying and breaking currents under normal circuit conditions and also making, carrying for a
specified time and breaking currents under specified abnormal circuit conditions such as those
of short-circuit (IEC 60947-2). They thus also fulfill the requirements of (load) switches. Circuit
breakers are often designed so that they can fulfill the requirements for disconnectors.
2.2.1.5 Supply disconnecting devices
IEC 60204-1 (Machine safety – Electrical equipment of machines) requires a supply disconnect-
ing (isolating) device for each incoming source of supply and for each on-board power supply
that completely isolates the machine or the device from the external or internal power supply for
the machine, so that cleaning, maintenance and repair work can be carried out or the machine
can be shut down for longer periods of time.
- A supply disconnecting device must fulfill the requirements of a switch-disconnector as
defined in IEC 60947-3 (load switch with isolating function) and at the least fulfill the require-
ments of utilization categories AC-23B or DC-23B. Disconnectors are permitted if load shed-
LVSAM-WP001A-EN-P - April 2009 2-3