Instructions

30 GMC-I Messtechnik GmbH
Settings for Short-circuit current Calculation – Parameter I
K
Short-circuit current I
K
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
K
must be
greater than tripping current Ia (see table 6 in section 21.1). The
variants which can be selected with the “Limits” key have the fol-
lowing meanings:
I
K
: Ia The measured value displayed for I
K
is used without
any correction to calculate Z
L-N
.
I
K
: Ia+Δ% The measured value displayed for Z
L-N
is corrected by
an amount equal to the test instrument’s measuring
uncertainty in order to calculate I
K
.
I
K
: 2/3 Z In order to calculate I
K
, the measured value displayed
for Z
L-N
is corrected by an amount corresponding to all
possible deviations (these are defined in detail by VDE
0100, part 600, as Z
s(m)
≤ 2/3 x U
0
/Ia).
I
K
: 3/4 Z Z
s(m)
≤ 3/4 x U
0
/Ia
Z Loop impedance
I
K Short-circuit current
U Voltage at the test probes, “U
N
” is displayed if voltage Umax.
deviates from nominal voltage by 10%
f Frequency of the applied voltage,
“f
N” is displayed if frequency fmax. deviates from nominal fre-
quency by 1%
Ia Tripping current (see data sheet for circuit breakers / fuses)
Δ % Test instrument inherent error
Start Measurement
Display of U
L-N
(U
N
/ f
N
)
If the measured voltage value lies within a range of ±10% of the
respective nominal line voltage of 120 V, 230 V or 400 V, the
respectively corresponding nominal line voltage is displayed. In
the case of measured values outside of the ±10% tolerance, the
actual measured value is displayed.
Displaying the Fuse Table
After measurement has been performed, allowable fuse types can
be displayed by pressing the HELP key.
The table shows maximum allowable nominal current dependent
upon fuse type and breaking requirements.
Key: Ia = breaking current, I
K
= short-circuit current,
I
N
= nominal current, t
A
= tripping time
Semiautomatic measurement
See also section 5.8 regarding the
AUTO parameter. L-PE relationships are
not possible here. The neutral L-N rela-
tionship is not offered during automatic
sequencing to the right of the auto en-
try!
Polarity selection
Limit value:
I
K
< limit value
U
L
⏐ R
L
I
K