At which end should I ground the shield of a shielded cable?
The rule depends on the frequency of the noise. With high-frequency noise from an inverter (above 1 MHz) the shield is grounded at both ends; that is what is correct for the motor cable. With low-frequency noise and where there is a risk of an ground loop, grounding at one end is preferred. In both cases the shield must be connected with a 360 degree clamp.
Shield grounding is the most debated subject in the field, because there are two correct answers and which one applies depends on the frequency of the noise.
Grounding at both ends: this is correct for high-frequency noise. The shield forms a short path for the noise to return to its source. This method is always used on the cable between the inverter and the motor; if only one end is grounded the shield behaves like an antenna at high frequency. Its risk is the ground loop: if there is a potential difference between the two ends, current flows through the shield.
Grounding at one end: preferred for low-frequency interference and for measurement/analogue signals; it eliminates the ground loop completely. Usually the panel side is grounded and the field end is left free.
The details of the installation determine the outcome:
- Connect the shield with a 360 degree clamp. Twisting the shield and extending it with a single wire (a "pigtail") creates inductance at high frequency and largely ruins the protection.
- Keep the path between the shield and the ground bar short.
- Do not use the shield as a signal return conductor; the shield is for protection, not for conduction.
In receiver and antenna wiring, however, the most effective measure is still distance.
The full topic: Wireless remote control installation: pairing, relay, safety