18
2-4 APPLICATION AND SELECTION
The contactors should be selected according to the types of their loads. The loads are classified in IEC60947 as shown
in the following table, and include those of the transformer, condenser, etc. in other category. Table 13 provides
references for the selection of contactors.
Table 13. Reference for selection
Category Typical applications Selection
AC1 Non-inductive or slightly inductive
load, resistance furnaces
Refer to 2-4-3.
AC2 Slip-ring motors :
Starting , plugging
The same as paragraph 24-l
unless plugging is included.
AC3 Squirrel-cage motors :
Starting, switching off motors
during running
Refer to 2-4-1.
IEC
60947-4-1
AC4 Squirrel-cage motors:
Starting, plugging, inching
Refer to 2-4-2.
DC load Refer to 2-4-4.
Star-delta starter Refer to 2-4-5.
Condenser load Refer to 2-4-6.
Opening/closing of primary side of
transformer
Refer to 2-4-7.
2-4-1 Application of AC3
(1) Standard for selection
When controlling the motor by the contactor, the load current shown in Fig. 16 flows, so a contactor corresponding
to this current is selected. The key points of the selection are given in Table 14 according to the main items.
Fig. 16 Motor current
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