Cabling and EMC in Servo Systems: Rules That Work in the Field
Separating power from signal, 360° shield bonding, grounding, EtherCAT cabling, moving cables and filters: the source of most unexplained faults.
This content supports preliminary sizing and architecture decisions; it does not replace the selected product manual or machine risk assessment.
1. Separate power from signal
Motor power cables are a strong noise source because of the drive's fast switching. Run encoder, network, pulse and analog cables in separate ducts; where they must cross, cross at right angles.
- Avoid long parallel runs
2. Bond the shield over 360°
The motor-cable shield is bonded at the drive and at the motor with a wide-area clamp. A thin pigtail wire largely cancels the shield at high frequency.
- Paint is not ground; the clamp sits on bare metal
3. Grounding and the mounting plate
Inside the cabinet, drives, filters and shield clamps meet on a common conductive mounting plate. PE connections are short and of generous cross-section.
4. EtherCAT and network cables
Use shielded cable of at least Cat5e for EtherCAT; at most 100 m between two devices. The line runs in a separate duct from power cables and the connectors must be seated firmly. The ETG.1600 installation guideline gives these rules in detail.
5. Moving cables
Cables flexing in a drag chain must be of the flexible type designed for it; a fixed-installation cable breaks inside and first shows up as random encoder errors. Respect the minimum bending radius.
6. EMI filter and line reactor
An EMI filter stops the drive's noise from returning to the mains; a line reactor reduces harmonics and current surges. Both are mounted close to the drive and well grounded.
| Symptom | Likely cause | Check |
|---|---|---|
| Random encoder error | Power and encoder in one duct / fatigued cable | Cable route, chain-rated cable |
| EtherCAT working-counter error | Shield, connector, line length | Per-port error counters |
| Position drift with pulses | Noisy pulse line | Differential drive, shield |
| Creep on analog command | Ground difference, shield | Differential input, zero offset |
Frequently asked questions
Should the shield be bonded at one end or both?
On the motor power cable, at both ends with a wide-area clamp. For low-level analog signals it may be bonded at one end if a ground loop appears.
How long can an EtherCAT cable be?
At most 100 m between two devices.
Technical sources
Sources are publications from standards owners and manufacturers.