User Manual

20 GMC-I Messtechnik GmbH
1) Measuring Contact Current Without Tripping the RCD
Measuring Method
The instrument uses a measuring current of only 1/3 nominal
residual current for the determination of contact voltage U
IΔN
which occurs at nominal residual current. This prevents tripping of
the RCCB.
This measuring method is especially advantageous, because
contact voltage can be measured quickly and easily at any electri-
cal outlet without tripping the RCCB.
The usual, complex measuring method involving testing for the
proper functioning of the RCD at a given point, and subsequent
substantiation that all other systems components requiring pro-
tection are reliably connected at low resistance values to the
selected measuring point via the PE conductor, is made unneces-
sary.
N-PE Reversal Test
Additional testing is conducted in order to
determine whether or not N and PE are
reversed. The pop-up window shown at
the right appears in the event of reversal.
Attention!
!
Execute a data backup before starting measurement and
switch off all consumers in order to prevent the loss of
data in data processing systems.
Start Measurement
Amongst other values, contact voltage U
IΔN
and calculated earth-
ing resistance R
E
appear at the display panel.
Note
The measured earthing resistance value R
E
is acquired
with very little current. More accurate results can be
obtained with the selector switch in the R
E
position.
The DC + function can be selected here for sys-
tems with RCCBs.
Unintentional Tripping of the RCD due to Bias Current within the System
If bias currents should occur, they can be measured with the help
of a current clamp transformer as described in section 13.1 on
page 51. The RCCB may be tripped during the contact voltage
test if extremely large bias currents are present within the system,
or if a test current was selected which is too great for the RCCB.
After contact voltage has been measured, testing can be per-
formed to determine whether or not the RCCB is tripped within
the selected time limits at nominal residual current.
Unintentional Tripping of the RCD due to Leakage Current in the Measur-
ing Circuit
Measurement of contact voltage with 30% nominal residual cur-
rent does not normally trip an RCCB. However, the trip limit may
be exceeded as a result of leakage current in the measuring cir-
cuit, e.g. due to interconnected power consumers with EMC cir-
cuit, e.g. frequency converters and PCs.
2) Tripping Test after the Measurement of Contact Voltage
➭ Press the I
Δ N
key.
The tripping test need
only be performed at
one measuring point for
each RCCB.
If the RCCB is tripped at nominal residual current,
the MAINS/NETZ LED blinks red (line voltage disconnected) and
time to trip t
a
and earthing resistance R
E
appear at the display
panel.
If the RCCB is not tripped at nominal residual current,
the RCD/FI LED lights up red.
Contact Voltage Too High
If contact voltage U
IΔN
, which has been measured with 1/3 nomi-
nal residual current I
ΔN
and extrapolated to I
ΔN
, is > 50 V (> 25 V),
the U
L
/R
L
LED lights up red.
If contact voltage U
IΔN
exceeds 50 V (25 V) during the measuring
sequence, safety shut-down occurs.
Note
Safety Shut-down: At up to 70 V, a safety shut-down is
tripped within 3 seconds in accordance with IEC 61010.
Contact voltages of up to 70 V are displayed. If contact voltage is
greater than 70 V, U
IΔN
> 70 V is displayed.
Limit Values for Allowable, Continuous Contact Voltage
The limit for allowable, continuous contact voltage is U
L
=50V for
alternating voltages (international agreement). Lower values have
been established for special applications (e.g. medical applica-
tions: U
L
=25V).
Attention!
!
If contact voltage is too high, or if the RCCB is not
tripped, the system must be repaired (e.g. earthing resis-
tance is too high, defective RCCB etc.)!
3-Phase Connections
For proper RCD testing at three-phase connections, the tripping
test must be conducted for one of the three phase conductors
(L1, L2 and L3).
Inductive Power Consumers
Voltage peaks may occur within the measuring circuit if inductive
consumers are shut down during an RCCB trip test. If this is the
case, the test instrument may display the following message: No
measured value (– – – ). If this message appears, switch all power
consumers off before performing the trip test. In extreme cases,
one of the fuses in the test instrument may blow, and/or the test
instrument may be damaged.