Manual

56 Gossen Metrawatt GmbH
Special Case: Suppressing Display of the Limit Value
The limit value cannot be
ascertained. The inspec-
tor is prompted to evalu-
ate the measured val-
ues himself, and to
acknowledge or reject
them with the help of the
softkeys.
Measurement passed:
. key
Measurement failed:
key
The measured value can
only be saved after it has
been evaluated.
13.3 Settings for Calculating Short-Circuit Current
– Parameter I
SC
Short-circuit current I
SC
is used to test shutdown by means of an
overcurrent protective device. In order for an overcurrent protec-
tive device to be tripped on time, short-circuit current I
SC
must be
greater than tripping current Ia (see table 6 in section 25.1). The
variants which can be selected with the “Limits” key have the fol-
lowing meanings:
I
SC
:I
a
The measured value displayed for I
SC
is used
without any correction to calculate Z
L-PE
.
I
SC
:I
a
+% The measured value displayed for Z
L-PE
is cor-
rected by an amount equal to the test instrument’s
measuring and intrinsic uncertainties in order to
calculate I
SC
.
I
SC
: 2/3 Z In order to calculate I
SC
, the measured value dis-
played for Z
L-PE
is corrected by an amount corre-
sponding to all possible deviations (these are
defined in detail by IEC 60364-6 as
Z
s(m)
 2/3 × U
0
/I
a
).
I
SC
:3/4 ZZ
s(m)
 3/4 × U
0
/I
a
Z Loop impedance
I
SC
Short-circuit current
U Momentary voltage at the test probes, “U
N
” is displayed if
U
max.
deviates from nominal voltage by 10%
f Frequency of the applied voltage,
“f
N
” is displayed if frequency f max. deviates from nominal
frequency by 1%
I
a
Tripping current
(see data sheet for circuit breakers / fuses)
% Test instrument intrinsic error
Limit Value:
I
SC
< Limit Value
U
L
 R
L