Contact Voltage (Rcd Uc) - METREL MI 3122 Instruction Manual

MI 3122 Smartec Z Line-Loop / RCD
Connections for testing RCD
R
Ro
E
Figure 5.2: Connecting the plug commander and the universal test cable

5.1.1 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
RCD and then normalized to the rated I
Contact voltage measurement procedure
Select the
RCD

Set sub-function Uc.

Set test parameters (if necessary).

Connect test cable to the top of the instrument.

Connect test leads to the item to be tested (see figure 5.2).

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.
RCD type
AC
AC
A
A
A
A
.
N
function using the function selector switch.
Contact voltage Uc
proportional to
G
1.05I
S 21.05I
G
1.41.05I
21.41.05I
S
G
21.05I
221.05I
S
Table 5.1: Relationship between Uc and I
N
N
N
N
N
N
25
Testing RCD
L1
L2
L3
N
PE
N PE L
to avoid trip-out of the
N
Rated I
N
any
 30 mA
< 30 mA

N