The Impact of Excessive Cable Length in Brushless Motor Systems

In the engineering deployment of brushless motor systems (motor, drive, controller), the length of connecting cables is a critical design parameter. Cables exceeding the recommended length introduce significant parasitic parameters, leading to degraded electrical performance, compromised control stability, and increased reliability risks.

This article is divided into two parts, respectively examining the specific technical issues and mitigation strategies associated with excessive length in both the motor-to-drive power cables and the controller-to-drive signal cables.

I. Excessive Power Cable Length (Motor to Drive)

1. Increased Risk of Motor Burnout: The most hazardous issue. The inherent properties of excessively long cables generate high instantaneous voltage spikes. These spikes are directly applied to the motor windings, degrading insulation over time and potentially leading to short circuits and motor burnout.
2. Limited Motor Speed: Cables have inherent resistance, which increases with length. Higher resistance causes greater voltage drop along the cable when current flows, resulting in insufficient voltage at the motor terminals. This reduces output torque and maximum achievable speed.
3. Drive Fault Alarms: Voltage spikes and current fluctuations caused by the cable may be misinterpreted by the drive as overvoltage or overcurrent events, triggering unnecessary shutdowns and alarms.

II. Excessive Signal Cable Length (Controller to Drive)

1. Unstable Motor Operation: Long signal cables act as antennas, making them highly susceptible to electromagnetic interference (EMI) from nearby power cables. This can corrupt speed command signals, causing unstable motor speed and jerky motion.
2. Critical Signal Errors: Interference on Hall sensor feedback signals leads to inaccurate position sensing. Interference on critical switch signals (e.g., E-stop, Enable) can cause unintended starts or stops, creating serious safety hazards.
3. Communication Disruption: When using communication protocols (e.g., MODBUS) for control, long cables are prone to signal attenuation and interference. This can result in lost or delayed control commands, destabilizing the entire system.

Conclusion:

The guiding principle is shorter cables are better, provided installation requirements are met. When shortening cables is impossible, targeted countermeasures such as filtering, shielding, and isolation are essential.

Updated on: 29/12/2025