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Decision:0 n% O, ~+ s1 R; M, z
Measuring the protective earth connection has in fact two reasons. It is to determine impedance6 v$ m5 j4 y) ]3 e6 ~- u# U
and cross-sectional area of protective earth connections. For a measuring current of 25 A both ~) o8 u" z D, c& Z5 ?7 r* [$ E
can be done with one measurement. Requiring a measuring current of more than 25 A it shall be; e4 C1 }% h" [! Y
splitted up into two measurements. In this case, the impedance shall be determined first, using a
9 z; ]( z6 M7 O* x8 Gvoltage not exceeding 6 V.
% d3 A$ c5 D; T6 {( x' VIf cross-sectional area of the protective earth connections cannot be determined as equal to the; M0 A# ]# ?* s- v
one for the phase by measurement of the area, then measurement with current shall be from a
. u6 q: u9 A) gsource with a higher voltage than 6 V." H* p2 ]% n1 C Z0 |% f
Explanatory notes:
1 b+ I7 _: h$ G3 wA circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for8 ?) a1 g( u8 l# w: U# x2 O& }
example due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones. V' I+ Q! @6 s- V0 n) d# ^# D
because of their ability to flash through. In this case, the impedance shall be determined first,
' W3 x7 s: H0 j( U$ q t& _; W' Z/ Cusing a voltage not exceeding 6 V." i+ ?) M8 \& c4 \- F% P2 K
Using low voltages and low currents has a great impact on the accuracy of the measurement of
1 l, a% D, I0 p7 q4 Vlow impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated
$ Q2 {1 {7 t8 ?; T# rmeasuring device./ A4 ]7 E9 l9 m, d# G
The relation between rated current of the EQUIPMENT and measuring current is because to
4 n$ v2 J W9 I1 `- c9 V. o9 Rcheck cross-sectional areas of protective earth connections. If parts of the construction or printed
; y" _4 l0 L; z0 {: y! v. _; Gcircuit boards are used for protective earth connections the cross-sectional areas and the ability+ I: E, V2 P# p" r, y2 _
of carrying short circuit c urrents are in doubt. |
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