Insulation Resistance of Single Core Cable

  • The insulation of proper thickness over the conductor is provided in order to prevent leakage current. 
  • The leakage current is a current which flows in a path that don’t intend to provide to it. As the conductor is circular, the path of leakage current is radial.

Let us

  • Radius of the single core conductor of cable = r1
  • Internal sheath radius = r2
  • Length of cable = L
  • Resistivity of cable insulation = ρ


Let us consider very small thickness of insulation dx at radius x distance.

  • Area of leakage current flows = 2πxL
  • Length through leakage current flows = dx
  • Insulation resistance of layer dx = ρ ( dx / 2πxL )

Insulation resistance of cable




 R α ( 1 / L )

  • The insulation resistance is inversely proportional to length of cable. If the length of cable decreases, its insulation resistance increases and vice versa.

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