Last updated on 2023-10-09 2 mins. to read

The inductance of a cable consists of two parts:

  1. Self-inductance (L): The property of a conductor (or circuit) to oppose a change in current flowing through it.
  2. Mutual inductance (M): The phenomenon where a change in current in one conductor induces a voltage in a neighbouring conductor.

Both concepts play a role when calculating the inductance for multi-conductor systems like three-phase cables.

Single-Phase Cables: The Standard Formula

For single-phase cables, the inductance (L) formula aligned with IEC 60909 is:

L=μ02πlnDr+14 H/m


  • μ0​ is the permeability of free space.
  • D is the center-to-center distance between the conductors.
  • r is the radius of the conductors.

Three-Phase Cables: The Complexity of Multiple Conductors

For three-phase cables, the inductance matrix includes self and mutual inductance terms:


Factors to Consider

When calculating the inductance of a cable, it is important to consider all factors.  Some of the more common considerations include:

  1. Mutual Inductance: In a three-core cable, the cores induce a magnetic field on each other. This can be accounted for using more complex matrix methods to define the mutual inductance between cores.

  2. Shielding: The presence of a metallic shield can alter the inductive characteristics of the cable.

  3. Non-uniform Arrangement: If the cores are not equally spaced, a more complex geometric mean distance (GMD) method may be required.