Rockwell Automation 1398-DDM-xxx USE MNL/ULTRA 200 DIG.SERVO.DR - Manual (Page 116)

Publication 1398-5.0 – October 1998
7-6 Power Connections
Emergency Stop Wiring
An overlapping contactor may be inserted between the motor and the
drive for emergency stop purposes. The contactor must not simply
break the motor current, it also must switch a three phase resistive
load in parallel with the motor windings.
The three resistors provide dynamic braking. In addition, they prevent
continuous arcing at the main contacts when breaking DC currents,
such as when the motor stalls. Simply breaking the motor current can
result in high voltages due to motor inductance, which will cause
prolonged arcing in the contactor. In extreme cases, the prolonged
arcing could result in the contactor catching fire. An overlapping
contactor provides the required timing by engaging the braking
contactors before the drive contactors disengage.
Figure 7.3 depicts a contactor installation with resistive loads. Follow
these guidelines:
●
The resistor values should be one to four times the winding
resistance for good braking performance. Refer to Appendix F,
“Dynamic Braking Resistor Selection” for resistor sizing
equations.
●
Screen and ground cables should be connected as shown.
●
Shields should be unbraided (not a drain wire soldered to the
shield).
●
Connection lengths should be minimized.
●
Safety ground (GND) and shield connections are permanently
connected. This is essential for electrical safety.
●
EMC guidelines require connection of the shield at the point
where the contactor is inserted.
DC Bus
Terminals 5 and 6 have voltage present when AC power is applied to
the drive. The DC Bus LED also illuminates when voltage is present
on the terminals.