HT instruments SIRIUS87 - Manual (Page 80)

SIRIUS 87
EN - 78
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.
11.5. TEST OF RCD TRIPPING TIME (RCD, RCD/DC)
Purpose of the test is to check the real tripping time of the general RCDs (it does not apply
to the selective RCDs).
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.
ALLOWABLE VALUES
The tripping current shall range from ½I
n to I n .
NOTE:
Make reference to the notes of the previous chapter too.
To check whether significant leakage currents are present on the installation operate as
follows:
a) After deactivating all the loads effect the tripping current measurement and take note
of the value.
b) 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 "rcd" is displayed the installation leakage current
added to the current for contact voltage measurement (½I
 n
) causes the RCD tripping.