HT instruments MACROTEST 5035 - Manual (Page 73)

MACROTEST 5035
EN - 72
11.4. WORKING TEST OF RCDS (RCD, RCD/DC, RCD S, RCD/DC S)
Check whether general and selective RCDs have been installed and adjusted properly and
whether they maintain their features over the time. The check shall confirm that the RCD
trips at a current I
∆
lower than its rated working current I
∆n
and that the tripping time
meets, depending on the case, the following conditions:
• does not exceed the maximum time provided by the standards in case of general type
RCDs (according to table).
• is included between the minimum tripping time and the maximum one in case of
selective type RCDs (according to table).
The RCD test effected by means of the test key is aimed at preventing
“the gluing
effect” from compromising the working of the RCD which has been inactive for a long
time; therefore this test is effected only to verify the mechanical working of the RCD and it
does not permit to declare that the RCD is complying with the standards. According to a
statistical survey the periodical check, once a month, of the RCDs by means of the test
key reduces by one half the RCD fault rate, this test however detects only 24% of
defective RCDs.
INSTALLATION PARTS TO BE CHECKED
All the RCDs shall be tested when installed.
In the low voltage installations the test is recommended to grant an acceptable safety
level.
Note In case the earth installation is not available effect the test connecting the
instrument with one terminal on a conductor downstream the RCD and one
terminal on the other conductor upstream the RCD itself.
ALLOWABLE VALUES
To compare the measurements make reference to the table reporting the limits for the
tripping times. On each RCD it is necessary to effect: a test with leakage current in phase
with voltage and a leakage current phase shifted by 180° with respect to the voltage. The
highest time is to be considered as significant result.
The test at ½I
∆n SHALL NEVER cause the RCD tripping.
NOTE:
Before effecting the test at the RCD rated current the instrument carries out a test at ½I
∆n
to measure the contact voltage and the overall earth resistance; if during this test the RCD
trips the indication l
"rcd" is displayed. During this test the RCD may trip for three possible
reasons:
a) The RCD tripping current is lower than ½I
∆n .
b) An earth plate is already present on the installation which added to the earth
generated by the instrument causes the RCD tripping.
c) There is no earth installation.
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
Ω, this value for the TN and IT systems is not to be considered while for the
TT systems it is merely indicative.