MI 3101 EurotestAT: Measurements
Testing RCD
53
Circuits for testing RCD
L1
L2
L3
N
PE
R
E
Ro
L
PE
N
L/L
1
N/L2
PE/L3
Figure 5.13: Connecting the plug commander and the universal test cable
5.3.1 Contact voltage (RCD Uc)
A current flowing into the PE terminal causes a voltage drop on earth resistance, i.e.
voltage difference between PE equipotential bonding circuit and earth. This voltage
difference is called contact voltage.
The voltage is present on all accessible conductive
parts connected to the PE. It should always be lower than the conventional safety limit
voltage. The contact voltage is measured with a test current lower than ½ I
N
to avoid trip-
out of the RCD and then normalized to the rated I
N
.
Contact voltage measurement procedure
Select the
RCD
function.
Set sub-function
Uc.
Set test
parameters
(if necessary).
Connect
test cable to the instrument.
Connect
test leads to the tested object (see
figure 5.13
).
Press the
TEST
key.
After the measurement is finished
store
the result (optional).
Displayed contact voltage relates to the rated nominal residual current of the RCD and is
multiplied by appropriate factor. Common factor of 1.05 is applied to avoid negative
tolerance of result, additional depend on RCD type and type of test current. See table 5.1
for detailed contact voltage calculation.
RCD type
Contact voltage Uc proportional to
Rated I
N
AC G
1.05
I
N
AC
S
2
1.05
I
N
any
A G
1.4
1.05
I
N
A
S
2
1.4
1.05
I
N
30 mA
A G
2
1.05
I
N
A
S
2
2
1.05
I
N
< 30 mA
B G
2
1.05
I
N
B
S
2
2
1.05
I
N
any
Table 5.1: Relationship between Uc and I
N
