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11
ADDENDUM C
SANS 10142-1:2003
8.5 PROSPECTIVE SHORT CIRCUIT CURRENT (SEE SECTION 2 OF THE CERTIFICATE OF COMPLIANCE /
TEST REPORT)
8.5.1 Obtain the estimated prospective short-circuit current (PSCC) at the point of supply from the
supplier of electric.
8.5.2 In the case of supply systems rated at not more than 250V to earth, measure the PSCC at the point
of control with a commercially available instrument (fault current meter). Before any instrument
is connected, confirm that the instrument is rated for the applicable current rating, in particular
where the current rating at the main switch disconnector exceeds 100 A or the PSCC is expected
to exceed 10 kA.
Note 1: Do not measure three-phase PSCC if the meter is not specifically designed for that purpose
or for the capacity supply (or both). In a balanced three-phase system, the three-phase value can
be estimated by multiplying the single-phase value by 1.73.
Note 2: Ensure that the instrument connections do not add impedance to the circuit measured.
CAUTION: Verify the suitability and accuracy of the PSCC instrument with the manufacturer.
8.5.3 Information on three-phase PSCC can also be obtained from graphs, tables and computer
programs, suppliers of equipment, or can be calculated using the following formula:
V
3 x Z
total
Where V
=
the phase-to-phase voltage, in volts;
Z
total
=
the total impedance of the upstream network in ohms,
including, for example, the source transformer
impedance and the impedance of a phase conductor.
8.5.4 The source transformer impedance can be calculated using the following formula:
Z
transformer
=
V
2
x Z
%
P x 10
3
100
Where Z
transformer
=
the source transformer impedance;
P
=
the power of the transformer, in kilovolt amperes;
Z
%
=
the rated short-circuit impedance voltage of the
transformer expressed as a percentage
Summary of Contents for ACADEMY T419
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