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2.4 Warning for Residual High Voltages
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WARNING
In DC withstanding voltage testing and insulation resistance testing, the test lead
wire, test probe, and DUT are charged to a high voltage. The tester is equipped with a
discharge circuit, but some time is nonetheless required to discharge them after the output is
cut off. There is a danger of electric shock during discharge. To avoid electric shock, take the
utmost care to ensure that the DUT, test lead wire, probe, and highly charged parts around the
output terminal are not touched. If it is necessary to touch them, be sure to confirm both (1)
and (2):
(1) The analog voltmeter indicates “zero.”
(2) The DANGER lamp has gone out.
As soon as the output is cut off, the tester’s discharge circuit starts forced discharging. Do not
disconnect the DUT during a test or prior to completion of discharging.
Discharge time
The length of the discharge time varies according to the properties of the DUT.
Discharge is conducted at a resistance of approximately 2 k in DC withstanding
voltage testing, and at 10 k in insulation resistance testing.
When no DUT is connected, the tester itself requires the following lengths of time
to reduce the internal capacitor voltage to 30 V.
If the DUT is disconnected during a test or before the completion of discharging, assuming that
the DUT has a capacity of 0.01uF and a parallel resistance of 100 M, approximately 5.3
seconds at 5 kV and approximately 3.5 seconds at 1 kV are required for the DUT to discharge
to 30 V.
When the approximate time constant of the DUT is known, the time required for discharging to
30 V after the output is cut off is calculated as the time constant times the value given above.
2.5 Dangerous States of Failed Tester
Typical possible dangerous states of the tester are as shown below and in which cases the
most dangerous situation that
“the high test voltage remains delivered
and won't be
turned off!”
may occur. When this situation has occurred, immediately turn OFF the power
switch and disconnect the AC power cable from the AC line receptacle.
•The DANGER lamp does not go out despite you have pressed the STOP switch.
•The DANGER lamp does not light up despite the pointer of the analog voltmeter is
deflected indicating that the output voltage is being delivered.
Also when the tester is in other malfunctioning states than the above, there is a possibility
that the output voltage is delivered irrespective of your proper operating procedure. Never use
