KYORITSU 6010B - Manual (Page 16)

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Insulation resistance (MΩ) =
Test voltage (V)
Leakage current (µA)
As the capacitance of the system charges up, so the charging current falls to
zero and a steady insulation resistance reading indicates that the capacitance of
the system is fully charged. The system is charged to the full test voltage, and
will be dangerous if left with this charge. KEW 6010B provides an automatic
path for discharging current as soon as the test button is released to ensure that
the circuit under test is safely discharged.
If the wiring system is wet and/or dirty, the surface leakage component of the
leakage current will be high, resulting in low insulation resistance reading. In the
case of a very large electrical installation, all the individual circuit insulation
resistances are effectively in parallel and the overall resistance reading will be
low. The greater the number of circuits connected in parallel the lower will be
the overall insulation resistance.
6 ．2 Damage to Voltage-Sensitive Equipment
An increasing number of electronic-based items of equipment are being
connected to electrical installations. The solid state circuits in such equipment
are likely to be damaged by the application of the levels of voltage used to test
insulation resistance. To prevent such damage, it is important that voltage-
sensitive equipment is disconnected from the installation before the test is
carried out and reconnected again immediately afterwards. The devices which
may need to be disconnected before the test include:-
● Electronic fluorescent starter switches
● Passive infra-red detectors (PIRs)
● Dimmer switches
● Touch switches
● Delay timers
● Power controllers
● Emergency lighting units
● Electronic RCDs
● Computers and printers
● Electronic point-of-sale terminals (cash registers)
● Any other device which includes electronic components.
quickly falling to zero so that it has no effect on the measurement. A high
voltage is used because this will often break down poor insulation and cause
flashover due to surface leakage (see 6.1.4), thus showing up potential faults
which would not be present at lower levels. The insulation tester measures the
applied voltage level and the leakage current through the insulation. These
values are internally calculated to give the insulation resistance using the
expression:-