Insulation Resistance - Iso-Tech IMT-3300 Manuel D'instructions

Main switch open
Test at socket
Temporary Link
between L and E
Typical arrangement for measuring the continuity of protective
conductors.
 Warning! Verify the circuit is de-energised before testing.

4.2 Insulation resistance

When used as an insulation tester, the instrument is configured
to measure high values of resistance and hence the electrical
quality of the insulating material within the circuit. The insulation
tester applies a high voltage, measures the total leakage current
flow and displays the calculated resistance. A dc voltage is
used to eliminate leakage currents caused by capacitance in the
circuit. A steady insulation resistance reading will indicate that any
capacitance within the system is fully charged and the capacitive
leakage current has reduced to zero. Insulation resistance
measurement errors may be due to the circuit under test being wet
and/or dirty. Errors may also occur when testing large installations
where the insulation resistances may effectively be in parallel.
Fig 2
All fuses in or circuit
breakers closed Mains
switch open
Typical arrangement for insulation testing.
 Warning! Verify the circuit is de-energised before testing.
4.3 Loop Impedance
If an electrical installation is protected by over-current
protective devices including circuit breakers or fuses, the earth
loop impedance should be measured.
In the event of a fault, the earth fault loop impedance should
be low enough (and the prospective fault current high enough)
to allow automatic disconnection of the electrical supply by the
circuit protection device within a prescribed time interval.
Every circuit must be tested to ensure the earth fault loop
impedance value does not exceed that specified or appropriate
for the over-current protective device installed in the circuit.
— 7 —
Equipment disconnected
Lamps
Switches
removed
closed
Reading not less than 0.5 MΩ
Fig 3