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GMC-I Messtechnik GmbH
6.3.2
Differential Current Measurement for Protection Class I Devices
This test must be executed for all devices for which it is not possible to measure insulation
resistance at all safety relevant parts (practically all DUTs with electrically actuated switches
and relays), or where there is any doubt regarding measurement with insulation voltage, for
example at electronic devices. If the DUT is equipped with a non-polarized mains plug, the
test must be performed with the mains plug poled in both directions. The measurement of
residual current includes the sum of instantaneous current values in L1, L2, L3 and N.
Attention
!
!
The DUT is placed into operation, and this test may not be performed until the
protective conductor test has been passed.
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Turn off the device under test.
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Plug the DUT into the appropriate surface mount socket (15, 17, 18) at the test case.
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Set the L1/L2/L3 switch (2) to “L1”.
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Set the NETZ-VDE switch (1) to “NETZ”.
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Signal lamps L1, L2 and L3 (19) indicate the presence of line voltage.
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Place the device under test into service by switching it on.
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Set the measuring function selector switch (6) at the METRATESTER 5+ test instrument
to the “I
Diff
20 mA” position and read the differential current value in mA from the display
at the test instrument.
The limit value is 3.5 mA, or 1 mA per kW of heating power for DUTs with heating elements
with a with a total connected load of greater than 3.5 kW.
Note!
For devices with permissible protective conductor current of greater than 3.5 mA in
accordance with the device standards, special protective conductor connection must
be observed and the following warning sign must be present: “High leakage current!
– connect protective conductor before connecting to the mains” (DIN 4844).
Measurements must be performed with the mains plug poled in both positions (if the
plug is reversible). The larger of the two measured values is deemed valid. The
possibility of a symmetrical error must be taken into consideration with multi-phase
devices. Data cables, as well as gas and water supply lines with potential to ground,
for example, do not have to be disconnected from the DUT for this measurement.
If no device under test has been connected, numbers appear at the digital display which do
not represent any actual measured value.