Shielded Cable
A cable with a braided or foil metal layer placed around the conductors. The shield catches the electromagnetic field radiated by the motor cable and directs it to earth; this markedly reduces the noise coupled into the control lines and the receiver circuit.
The voltage at the inverter output changes by hundreds of volts in less than a microsecond. This fast change makes the motor cable work like an antenna. A shielded cable keeps this radiation inside the cable; when the shield is earthed, the noise current returns to its source by a controlled path.
- Where it is used: primarily on the motor cable. The biggest gain is here; limiting the noise at its source is more effective than trying to protect the control side.
- Continuity: the shield must not be interrupted at terminal boxes and intermediate connections. Twisting the shield like a thin wire into a long tail destroys most of the gain; prefer a 360° clamp.
- Together with: along with shielded cable, also apply the rules of at least approximately 20 cm separation between power and control cables and of right-angle crossings.
Moving the receiver and its antenna away from the inverter and the motor cable is, together with shielded cable, the most effective and cheapest pair of measures.
The context in which this term is used: Wireless remote control installation: pairing, relay, safety