The power stage of all modern motor controllers uses PWM voltages to control the motor power supply. Such PWM power signals can cause some EMI radiation and can negatively affect sensitive sensor signals (e.g. Hall sensors, analog sensors, video signals). Therefore, it is recommended to use shielded motor cables. This recommendation is especially important for 1. long motor cables, 2. motor cables close to sensor cables, and 3. high motor currents.
The shielding of the cable must be connected to earth on at least one side of the cable. If the cable length exceeds 1 or 2 meters, it is recommended to connect the shields at both ends of the cable to earth potential.
Solution:
The shield of the motor cable can be easily connected to the grounded part of a metal structure (e.g. cabinet or machine) by means of a so-called grounding clamp. The grounding clamps should be placed close to the controller and the motor. This is the same solution that is used for more powerful servo drives and inverters, and can also be used for maxon motors and controllers.
Strip off the insulation near the end of the motor cable. (usually within the last 10 cm of the cable).
Attach the grounding clip to the grounding metal tab of the cabinet or machine, close to the controller and motor.
Insert the shield of the cable into the grounding clip.
Important:
Ensure that the diameter of the grounding clip matches the diameter of the cable and that there is a tight and extensive contact between the cable shield and the grounding clip.
Additional Notes:
The grounding wires that may be used to connect different machine constructions or ground rods (fixed grounding clamps) have a sufficient cable cross-section. As a rule, the minimum cross section in use is 6 mm^2 (copper wire) and the maximum is 25 mm^2. Grounding cables with a cross section of 16 mm^2 are used quite commonly as a standard in machine manufacturers and electrical cabinets.
The ground contact is not blocked or limited by some anodized coating or paint, for example, if the contact is made by screws, nuts, cable tabs or washers used to contact the metal structure or housing of the motor.
The main point is that ground contacts, ground rods, ground wires and cable shields (and any connections between them) need to have a lower resistance (i.e. better conductivity) than any other GND contact or wire in the system. Equalization and stray currents always follow the line of least resistance, and these must be ground wires. A thick cross section and wide grounding/shielding contacts ensure that the current and potential balance actually passes through the ground rod, metal structure and ground wire. Finally, any contact point should have the same ground potential, which can be achieved by extremely low wire and connector resistance and the resulting minimum voltage drop in the ground path.
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