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Decision:0 F, b6 r- S! e8 R& T
Measuring the protective earth connection has in fact two reasons. It is to determine impedance( F: t9 G+ U0 G" l+ Y m/ z
and cross-sectional area of protective earth connections. For a measuring current of 25 A both
; P3 @* Z4 a3 l3 b. F- |can be done with one measurement. Requiring a measuring current of more than 25 A it shall be4 j( ]1 i: K5 v( U9 n
splitted up into two measurements. In this case, the impedance shall be determined first, using a- _) c+ z8 L$ B `1 G
voltage not exceeding 6 V.0 {6 J0 w' y1 R, r5 |9 d; F
If cross-sectional area of the protective earth connections cannot be determined as equal to the8 `* q6 v2 o. ]7 a/ L
one for the phase by measurement of the area, then measurement with current shall be from a
& @6 o& a: S* g9 V+ {) }6 W/ \7 Zsource with a higher voltage than 6 V.
" D& N' I+ d. v( |! T- s B& r5 n, CExplanatory notes:3 t# Q( W5 q5 M
A circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for
5 M4 z& i% A1 S8 n: ?example due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones e0 ^( j5 i8 r( K* F6 ^) B
because of their ability to flash through. In this case, the impedance shall be determined first,2 D& @ K% \! ?0 M
using a voltage not exceeding 6 V.
# m1 m0 j5 r" x$ N! {Using low voltages and low currents has a great impact on the accuracy of the measurement of) D, T+ a% c! F5 y" [5 q# l
low impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated* v- w! R {5 Z3 v
measuring device.
, `9 n: c( f- AThe relation between rated current of the EQUIPMENT and measuring current is because to
0 f- r1 ~3 l; l; m9 R. R, rcheck cross-sectional areas of protective earth connections. If parts of the construction or printed
2 [3 a4 Z0 _; R9 I! \, S* qcircuit boards are used for protective earth connections the cross-sectional areas and the ability% Q6 b2 h) s7 |8 C. |
of carrying short circuit c urrents are in doubt. |
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