User Manual

26 GMC-I Messtechnik GmbH
7.4 Testing Residual Current Circuit Breakers in TN-S Systems
Connection
RCCBs can only be used in TN-S systems. An RCCB would not
work in a TN-C system because PE is directly connected to the
neutral conductor in the outlet (it does not bypass the RCCB).
This means that residual current would be returned via the RCCB
and would not generate any differential current, which is required
in order to trip the RCCB.
As a rule, the display for contact voltage is also 0.1 V, because
the nominal residual current of 30 mA together with minimal loop
resistance results in a very small voltage value:
7.5 Testing of RCD Protection in IT Systems with High Cable
Capacitance (e.g. in Norway)
The desired system type (TN/TT oder IT) can be selected for RCD
test type U
IΔN
(I
ΔN
, t
a
), and for earthing measurement (R
E
).
A probe is absolutely essential for measurement in IT systems,
because contact voltage U
IΔN
which occurs in these systems
cannot otherwise be measured.
After selecting the IT system setting, connection with probe is
selected automatically.
Set the Parameter – Select System Type
Start Measurement
UIΔNR
E
IΔN• 1Ω 30mA⋅ 30mV 0
·
03V,== ==
System
type: