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6. INSULATION RESISTANCE MEASUREMENTS
6.1. Measurements at 200M
Ω
/250V
This is the voltage used for the majority of insulation resistance tests on
normal installation requirement. To measure insulation resistance, press
the test button to power on the tester. The LCD will displayed the
insulation resistance. Section VII indicated that subdivision of large
installations might be necessary because of the large number of parallel
insulation resistance. In such a case, an installation may be divided into
sections, each being separately tested. Each section must have not less
than fifty outlets, an outlet being a switch, socket, lighting point etc. A
switched socket counts as one outlet. The minimum acceptable
insulation resistance is 1MΩ. For a large installation, the capacitance of
the insulation will be high, and it will take longer for it to become
charged by the direct testing voltage. Care must be taken not to take a
reading until there is a steady reading, indicating that the charging
process is complete.
Note:
The charge stored in the insulation will be discharged
automatically when the test button is released. Be careful not to turn
the range switch knob whilst the test button is pressed, or the
instrument will be damaged.
6.2. Measurements at 2000M
Ω
/1000V
Some specifications require testing at 1000V. This voltage must also be
selected where the supply voltage of the installation is between 500V
and 1000V. First, set the range switch to 1000V and then proceed as
indicated in a above for 500V testing. The above note also applies to
testing at 1000V. In addition the following applies.
Note: Make sure that the circuit under does not include components
Which will be damaged by the 1000V applied. Many normal components
of an installation are likely to be damaged if tested at 1000V. Examples
are power factor correction capacitors, low voltage mineral insulated
cables, electronic light dimmers, electronic ballasts and starters for
fluorescent lamps etc…
6.3. Lock power on Feature
For hands free operation a lock power on feature is incorporated on the
press to test button. Set LOCK button to lock test voltage, Pressing it
again will switch it off.
