KYORITSU 6016 - Manual (Page 23)

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8. INSULATION TESTS
 WARNING
Ensure that circuits to be tested are not live.
Disconnect the instrument from the circuit under test before operating the
function switch.
To select the insulation resistance range select ‘INSULATION’.
8.1.1 The nature of insulation resistance
Live conductors are separated from each other and from earth metal by insulation,
which has a resistance which is high enough to ensure that the current between
conductors and to earth is kept at an acceptably low level. Ideally insulation resistance
is infinite and no current should be able to flow through it. In practice, there will normally
be a current between live conductors and to earth, and this is known as leakage current.
This current is made up of three components, which are:-
1. capacitive current
2. conduction current, and
3. surface leakage current.
8.1.2 Capacitive Current
The insulation between conductors which have a potential difference between them
behaves as the dielectric of a capacitor, the conductors acting as the capacitor plates.
When a direct voltage is applied to the conductors, a charging current will flow to the
system which will die away to zero (usually in less than a second) when the effective
capacitor becomes charged. This charge must be removed from the system at the
end of the test, a function which is automatically performed by the KEW6016. If
an alternating voltage is applied between the conductors, the system continuously
charges and discharges as the applied voltage alternates, so that there is a continuous
alternating leakage current flowing to the system.
Fig.15