MI 3000 EasiPLUS Measurements
31
Test current starting polarity can be started with the positive half-wave at 0
0
or with the
negative half-wave at 180
0
.
positive start polarity
(0°)
negative start polarity
(180°)
Figure 5.13: Test current started with the positive or negative half-wave
5.3.5 Testing selective (time-delayed) RCDs
Selective RCDs demonstrate delayed response characteristics. Trip-out performance is
influenced due to pre-loading during measurement of contact voltage. In order to
eliminate the pre-loading a time delay of 30 s is inserted before performing the trip-out
test.
5.3.6 Contact voltage
Leakage current flowing to the PE terminal causes a voltage drop across earth
resistance, which is called contact voltage (Uc). This voltage is present on all accessible
parts connected to the PE terminal and should be lower than the safety limit voltage.
The parameter contact voltage is measured without tripping-out the RCD. R
L
is a fault
loop resistance and is calculated as follows:
N
C
L
I
U
R
Displayed contact voltage relates to the rated nominal differential current of the RCD
and is multiplied by a safety factor. See the table 5.1 for detailed contact voltage
calculation.
RCD type Contact voltage Uc
G
G
Uc 1.05I
N
S
S
Uc 1.052I
N
G
G
Uc 1.05
2
I
N
S
S
Uc 1.052 2 I
N
Table 5.1: Relationship between Uc and I
N
For additional general information concerning contact voltage measurement refer to
Metrel’s handbook Measurements on electric installations in theory and practice.
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