Kewtech KT64, Instruction Manual, Page: 22 / 44

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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. The KT
64 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.
8 . 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.
8 . 3 Preparation for measurement
Before testing, always check the following:-
1 The low battery Indication is not displayed
2 There is no visually obvious damage to the tester or to the test leads
3 Test the continuity of the test leads by switching to continuity test and
shorting out the lead ends. A high reading will indicate that there is a faulty
lead or that the fuse is blown.
Insulation