KYORITSU 6050 User Manual
Page 19
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Practical example of verification of the protection is a TT system
according to the international Standard IEC 60364.
Fig.12
The maximum value of Zs for this example is 2.1Ω(16amp gG fuse,0.4
seconds).The loop tester reads 1.14Ωand consequently the condition
Zs<_Uo / la is met.
5.1.2 Principles of the Measurement of Line Impedance and
Prospective Short Circuit Current
Line impedance is the impedance, which is measured between Phase-
terminal L and Neutral-terminal N of single-phase system, or between
two phases of three-phase system. Measurement principal used in this
instrument is the same as it for Fault loop impedance measurement, but
measurement is performed between Terminal L and N, or between two
phases.
Breaking current capacity of installed over-current protection devices
should be higher than Prospective Short-Circuit current, otherwise it is
necessary to change the rated current of involved over-current
protection device.