How much distance should I leave between the motor cable and a signal or RF cable?
The practical rule is to leave at least 50 mm of separation between motor and supply cables and analogue/low-level signal cables. If they have to cross, cross them at a 90 degree angle and do not share a long parallel route. As the separation distance grows, magnetic coupling falls off rapidly.
Interference arrives by two paths: capacitive coupling between conductors (fast voltage change) and magnetic coupling (fast current change). Both are high on a motor cable. What matters more than the distance is the length run in parallel; two cables running side by side for 30 cm cause far less trouble than ones running side by side for 3 m.
Practical layout for panel and in-vehicle applications:
- Use separate ducts/spiral wrap for power and signal, and do not let them share the same terminal row.
- Use a 90° angle at unavoidable crossings; with this geometry the coupling area is at its minimum.
- Place the RF receiver antenna as far as possible from the motor cable and from contactor and relay coils, on top of a metal mass.
- Run the analogue command line (for example the PT500's E analogue input or the KS250's IN5 analogue input) with twisted and, if needed, shielded cable.
- Separate the signal return from the power return and join them at a single point.
Even a few hundred millivolts of noise on the analogue reference can cause jitter in the speed setting or false triggering of the current-threshold stop function; that is why solving the separation at the wiring stage is more effective than adding filters afterwards.
Full topic: DC Motor Driver Selection Guide