5.6 Contact Voltage and Earthing
Resistance Test
The instrument UNITEST 0100-ELECTROcheck
tests the contact voltage and the earthing resistance
in systems with built-in residual current devices,
without RCD tripping. The test is performed at a test
current of approx 1/3 Idn (33%) of nominal fault
current. Hereby, the contact voltage present at the
protective conductor (PE) is measured.
Simultaneously, the earthing resistance of the loop
L-PE is calculated. Here, the contact voltage mea-
sured is divided by the nominal fault current
(RE=UB/I
Δ
N).
In accordance with the nominal fault current set via
the residual current circuit breaker, the maximum
earthing resistance is monitored in addition to the
contact voltage measured. Please refer to the fol-
lowing table for the maximum limit values:
Nominal Fault Current
I
Δ
N
30 mA 100 mA 300 mA 500 mA
Limit value of
contact voltage
25 V
25 V
25 V
25 V
Limit value of
earthing resistance
800
Ω
250
Ω
80
Ω
50
Ω
Table 1: Limit values for earthing resistance values
When testing residual current circuit breakers,
please respect the references indicated in sec-
tion 5.5. ‘General Information Regarding RCD
Tests’.
Performing the Measurement
Connect the desired test lead (either test lead with
shockproof plug or three individual test leads) to
the test instrument. Connect the black test lead
to the black socket 'L/L1' (24), the blue test lead
to the blue socket 'N / L2' (25), and the green test
lead to the green socket 'PE / L3' (26).
Switch on the UNITEST 0100-ELECTROcheck
using the rotary switch 'Measurement Function'
(19). In accordance with the respective nominal
fault current of the RCD under test select the ap-
propriate measurement function using the rotary
switch, e.g. 'RCD 30 mA'. The test instrument
displays as follows:
Figure 5.6.1: Instrument ready for operation
Now connect the test leads to the UUT. For cor-
rect connection, please refer to Figure 5.6.2 or
Figure 5.6.3.
23
Contact Voltage and Earthing Resistance Test
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