MI 3125 / BT EurotestCOMBO Measurements
38
Connections for testing RCD
Figure 5.17: Connecting the plug commander and the 3-wire test lead
5.4.1 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 and is present on all accessible conductive parts
connected to the PE. It shall 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
* model MI 3125 BT
Select the RCD function using the function selector switch.
Set sub-function Uc.
Set test parameters (if necessary).
Connect test cable to the instrument.
Connect test leads to the item to be tested (see figure 5.17).
Press the TEST key to perform the measurement.
Store the result by pressing the MEM key (optional)*.
The contact voltage result relates to the rated nominal residual current of the RCD and
is multiplied by an appropriate factor (depending on RCD type and type of test current).
The 1.05 factor is applied to avoid negative tolerance of result. See table 5.1 for detailed
contact voltage calculation factors.
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