400 Series
EN - 77
Before effecting the test at the RCD rated current the instrument carries out a test at ½IdN
to measure the contact voltage and the overall earth resistance; if during this test the RCD
trips an error message is displayed. During this test the RCD may trip for three possible
reasons:
the RCD tripping current is lower than ½ IdN
an earth plate is already present on the installation which added to the earth generated
by the instrument causes the RCD tripping.
If during measurement of contact voltage the voltage detected is higher than the safety
value (50V or 25V) the test is interrupted; proceeding with the test under such conditions
would mean to keep the contact voltage applied to all the metal masses connected to the
earth for a too long time resulting to be dangerous.
Among the test results of the RCD tripping time also the earth resistance value R
a
is
displayed in , this value for the TN and IT systems is not to be considered while for the
TT systems it is merely indicative.
13.5. TEST OF RCD TRIPPING CURRENT
13.5.1. Purpose of the test
Check the real tripping current of the general RCDs (it does not apply to the selective
RCDs).
13.5.2. Installation parts to be checked
When facing RCDs with tripping current to be selected it is useful to effect this test to
check the real RCD tripping current. For RCDs with fixed differential current this test can
be effected to detect any leakage of the installation users. In case the earth installation is
not available effect the test connecting one instrument’s terminal on a conductor
downstream the RCD and one terminal on the other conductor upstream the RCD itself.
13.5.3. Allowable values
The tripping current shall range from ½ IdN to IdN.
13.5.4. Note
Make reference to the notes of the § 13.4.4 too. To check whether significant leakage
currents are present on the installation operate as follows:
After deactivating all the loads effect the tripping current measurement and take note of
the value
Activate the loads and effect a new measurement of the tripping current; if the RCD
trips with a lower current, the installation leakage is the difference between the two
tripping currents. If during the test the error message is displayed the installation
leakage current added to the current for contact voltage measurement (½IdN) causes
the RCD tripping.
This test is not usually performed to compare the tripping time of the switch with the limits
prescribed by the standards. In this mode, the instrument detects the exact current and the
differential switch’s tripping time with the tripping current. Instead, the standards refer to
maximum tripping times in case the differential switch is tested with a leakage current
equal to the nominal current.
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