Guidelines for planning the electrical installation 73
Using a contactor between the drive and the motor
Implementing the control of the output contactor depends on how you select the drive to
operate.
When you have selected to use DTC motor control mode and motor ramp stop, open the
contactor as follows:
1. Give a stop command to the drive.
2. Wait until the drive decelerates the motor to zero speed.
3. Open the contactor.
When you have selected to use DTC motor control mode and motor coast stop, or scalar
control mode, open the contactor as follows:
1. Give a stop command to the drive.
2. Open the contactor.
WARNING! When the DTC motor control mode is in use, never open the output
contactor while the drive controls the motor. The DTC motor control operates
extremely fast, much faster than it takes for the contactor to open its contacts.
When the contactor starts opening while the drive controls the motor, the DTC control will
try to maintain the load current by immediately increasing the drive output voltage to the
maximum. This will damage, or even burn the contactor completely.
Protecting the contacts of relay outputs
Inductive loads (relays, contactors, motors) cause voltage transients when switched off.
The relay contacts on the drive control unit are protected with varistors (250 V) against
overvoltage peaks. In spite of this, it is highly recommended that inductive loads are
equipped with noise attenuating circuits (varistors, RC filters [AC] or diodes [DC]) in order
to minimize the EMC emission at switch-off. If not suppressed, the disturbances may
connect capacitively or inductively to other conductors in the control cable and form a risk
of malfunction in other parts of the system.
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