Inductive coupling

Definition

The disturber and the victim are coupled by a magnetic field. The level of disturbance depends on the current variations (di/dt) and the mutual coupling inductance.

Inductive coupling increases with:

• The frequency
• The proximity of the disturber to the victim and the length of the parallel cables,
• The height of the cables with respect to a ground referencing plane,
• The load impedance of the disturbing circuit.

Examples

(see Fig. R36)

• Nearby cables subjected to rapid current variations (di/dt)
• Short-circuits
• Fault currents
• Lightning strikes
• Stator control systems
• Welding machines
• Inductors

Fig. R36 – Example of inductive coupling

Counter-measures

• Limit the length of parallel runs of disturbers and victims to the strict minimum
• Increase the distance between the disturber and the victim
• For two-wire connections, run the two wires as close together as possible
• Use multi-core or touching single-core cables, preferably in a triangular layout
• Position a PEC bonded at both ends and between the disturber and the victim
• Use symmetrical transmission systems on correctly implemented, symmetrical wiring systems
• Shield the disturbing cables, the victim cables or both (the shielding must be bonded)
• Reduce the dv/dt of the disturber by increasing the signal rise time where possible (series-connected resistors or PTC resistors on the disturbing cable, ferrite rings on the disturbing and/or victim cable)