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Decision:/ M& n; P8 ~. S! U8 \1 {2 n+ |
Measuring the protective earth connection has in fact two reasons. It is to determine impedance
& I0 N+ l7 j1 A) m L5 ^- `7 A: _7 qand cross-sectional area of protective earth connections. For a measuring current of 25 A both
" \ A! w/ T4 D0 M9 n3 S: k3 dcan be done with one measurement. Requiring a measuring current of more than 25 A it shall be
/ F: X4 d$ `% ~+ E7 F; {4 q! ysplitted up into two measurements. In this case, the impedance shall be determined first, using a
- \7 s1 `9 h9 v/ Zvoltage not exceeding 6 V.
& u: L1 n0 x v2 f# {If cross-sectional area of the protective earth connections cannot be determined as equal to the
! s* z' ]' [8 y1 u+ |4 Qone for the phase by measurement of the area, then measurement with current shall be from a3 Z( A: m4 ?* H1 ~$ M
source with a higher voltage than 6 V.' k( ~2 Z- L" f/ Z4 x$ O
Explanatory notes: @. U: S% Q" d% B0 I# t
A circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for- D. ~/ T$ W/ [! d8 J2 j
example due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones
4 K* k; x" |2 N9 ] d7 e+ xbecause of their ability to flash through. In this case, the impedance shall be determined first,
4 R& o( u$ N P8 Ausing a voltage not exceeding 6 V.
. e7 T, v r6 r# _, {) F3 `* v/ [Using low voltages and low currents has a great impact on the accuracy of the measurement of$ c0 P( S4 }5 I/ `$ G/ {
low impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated
* D' w0 J% q' l7 S9 P# wmeasuring device.# m2 R. `" P \; v
The relation between rated current of the EQUIPMENT and measuring current is because to4 b8 s5 x0 j+ w6 u! z: ^ W
check cross-sectional areas of protective earth connections. If parts of the construction or printed
4 @4 r/ s# }, C9 Y" Bcircuit boards are used for protective earth connections the cross-sectional areas and the ability3 O$ q# y& l* H& P, U% ]
of carrying short circuit c urrents are in doubt. |
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