5
Instructions for Evaluating Insulation Integrity
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W A R N I N G !!!!!!!
C A U T I O N
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EXTREME CARE REQUIRED WHEN using the insulation breakdown test function. This is a
controlled voltage ‘Megger’ test where typically 500V is applied to the output pins for a preset period
(100milliseconds) while the microcomputer monitors the resistance to earth. The test is an automated
sequence and an indicative measurement is displayed on the LCD.
Step 1:
DISCONNECT THE LOOP AND FEEDER FROM ALL OTHER EQUIPMENT IN THE CABIENT.
THE HIGH VOLTAGE ASSOCIATED WITH THIS TEST WILL DAMAGE THE SENSITIVE
ELECTRONIC CIRCUITRY ASSOCIATED WITH VEHICLE DETECTION.
Step 2:
Make sure the TESTER is switched OFF – verify the LCD display is BLANK
Connect the RED lead to a single loop wire. Connect the Black wire to an appropriate EARTH
connection point.
Step 3:
Switch on the device and select the insulation integrity test. Select the test function again and an
audible ‘click from the relay switching will be displayed.
The device will generate the 500V pulse required by the test for a sustained period to enable a
resistance measurement to be determined. An indicative insulation resistance will be displayed on the
LCD display. The qualification for what is a PASS or FAIL is done by the operator to eliminate test
variables associated with the same loop and battery level. This is not a laboratory instrument and the
measurement is an indicative measurement.
This instrument has been Factory Test Certified at the following levels of resistance;
10MegOhm (±5%), 50MegOhm (±5-10%) and 200MegOhm (±10%). A resistor network composed of
0.5watt 10MegOhm resistors is used for this test. It is acknowledged that the environment is
reasonably stable and percentage tolerance in resistor values may impact on this test.
Insulation Integrity Test Range
Resistance =< 10Megohm
Indicates a resistance less than 10MegOhm
Resistance > 10MegOhms
Indicates a resistance greater than 10 MegOhm but less than 200MegOhms
Resistance > 200MegOhms
Indicates a resistance greater than 200MegOhms
The measurement range displayed by the instrument allows the operator to make an informed decision
about the loops insulation integrity as different road authorities have stated variations in accepted
winding to earth insulation resistance thresholds.
Note on Insulation Resistance Measurement
The calibration of the instrument provides for a higher tolerance in the resistance range of 5 to 15
MegOhms. The instrument performance significantly decreases in the range less than 5MegOhms.
The Insulation Resistance measurement is an indicative measurement of the nominal state of the loop.
The objective of this test function is to provide an objective TEST OK or FAIL status for the loop and
feeder cable. Variations in battery level capacity and rapid repetitive testing producing accumulated
mutual capacitance resulting from moisture ingress in the cable and field joints will effect readings.
Laboratory testing indicated that the same loop measured after a days rain, 4 hours since the last rain
fell and on a dry day will indicate three different resistance readings.
