11
Breakdown mode / burn mode
The insulation resistance ‘IR’ test operates
in either ‘Breakdown’ or ‘Burn’ mode.
Default mode is
breakdown
.
Left and right arrow buttons toggle between
burn and breakdown mode when a voltage
range is selected. Press and hold left
arrow/burn to activate burn mode.
In breakdown mode the test will automatically terminate on
detection of a breakdown to prevent damage to the insulation.
Burn mode disables the normal breakdown detection and
test voltage continues after breakdown of the insulation.
This enables the location of the failure to be seen and
detected acoustically but it is a destructive test.
Due to the potential damage that could occur, the unit
produces two long beeps when starting a test with burn mode
activated.
Running an insulation test
Before testing any reactive load the insulation must be
fully discharged.
15 kV - The functional earth
terminal
(
g
g
g
g
)
must be
connected to ground or a uni-potential bonding point.
Great care should always be taken when connecting the leads
to a system to be tested. Even isolated systems may exhibit
charges or induced voltages and appropriate Safe Working
Practices must be employed.
On connection of the test leads prior to starting a test, any
voltages of 50 V or more will be indicated on the display,
accompanied by an intermittent beeper, (see Voltmeter pg. 9).
This is especially likely in electrically noisy environments.
Should electrical noise be present it will cause a current to flow
through the instrument’s internal discharge resistors. If this
becomes excessive and exceeds instrument rating, damage to
the instrument may result.
The MIT1525 has been designed to handle high noise currents
up to 6 mA. If current above 6 mA is detected, the instrument
will sound an urgent “warble” tone and be accompanied by the
symbols
G
.
The instrument should be immediately disconnected from the
supply after discharging the dc test voltage taking care to
ensure Safe Working Practices. (NB very high induced
voltages may be present)
To assist user safety, the instruments will not permit a test to
be started if the induced voltage exceeds 6 mA.
It is possible to adjust the test voltage using the up and down
arrow buttons, either before or during a test. Once a test has
begun, it is advisable to only adjust the voltage in the first 10s
of the test to prevent interference with the capacitive and
absorptive currents in the insulator.
A test can be started by pressing the ‘TEST‘
button for approximately 3 seconds from the test
screen or voltmeter screen. A timer will be
displayed to indicate elapsed time during the
test. The test is stopped, by pressing the TEST button. As
soon as the test is stopped a discharge of the insulator is
automatically initiated. An ‘StP’ indication informs the user that
the test is terminating and after a few seconds the voltage on
the terminals will be displayed. Left and right arrows can be
used to scroll between terminal voltage, last test voltage and
TEST
