HT instruments SIRIUS89N - Manual (Page 117)

SIRIUS89N
EN - 115
EXAMPLE FOR EARTH RESISTANCE TEST
Let’s assume an installation protected by a 30 mA RCD. Let’s measure the earth
resistance using one of the methods quoted above, to evaluate whether the installation
resistance is complying with the standards in force and multiply the result by 0.03A (30
mA). If the result is lower than 50V (or 25V for special rooms) the installation can be
considered as co-ordinated as it respects the above-said relation.
When we face 30 mA RCDs (the most of civil installations) the maximum earth
resistance allowed is 50/0.03=1666
Ω permitting to use even simplified methods which
even though they do not provide extremely precise values give a value approximate
enough for the calculation of the co-ordination.
16.5. Working Test of RCDs (Rcd, Rcd/Dc, Rcd S, Rcd/Dc S)
PURPOSE OF THE TEST
Check (standards CEI 64-8 612.9, CEI 64-14 2.3.2.2.) 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 RCDs of
general type (according to
Table 3).
• is included between the minimum tripping time and the maximum one in case of
RCDs of selective type (according to Table 3).
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.
For the medical rooms this check shall be effected periodically every six months on
all RCDs according to the standards CEI 64-4 5.2.01 and CEI 64-13.
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 5 reporting the limits for
the tripping times. On each RCD it is necessary to effect: a test with leakage current in