HT Italia GSC53N, Instruction Manual

Page: 136 / 152

GSC53N - GSC57 - ZG47
EN - 134

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 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.
17.5. Working Test of Rcds (Rcd, Rcd/Dc, Rcd S, Rcd/Dc S)
PURPOSE OF THE TEST
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 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.
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.