21
8.1.3 Conduction Current
Since the insulation resistance is not infinite, a small leakage current flows through the
insulation between conductors. Since Ohm's Law applies, the leakage current can be
calculated from
8.1.4 Surface Leakage Current
Where insulation is removed, for the connection of conductors and so on, current will flow
across the surfaces of the insulation between the bare conductors. The amount of leakage
current depends on the condition of the surfaces of the insulation between the conductors.
If the surfaces are clean and dry, the value of the leakage current will be very small. Where
the surfaces are wet and/or dirty, the surface leakage current may be significant. If it
becomes large enough, it may constitute a flashover between the conductors.
Whether this happens depends on the condition of the insulation surfaces and on the applied
voltage; this is why insulation tests are carried out at higher voltages than those normally
applying to the circuit concerned.
8.1.5 Total Leakage Current
The total leakage current is the sum of the capacitive, conduction and surface leakage
current described above. Each of the currents, and hence the total leakage current, is
affected by factors such as ambient temperature, conductor temperature, humidity and the
applied voltage.
If the circuit has alternating voltage applied, the capacitive current (8.1.2) will always be
Fig.16
Fig.17
