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Decision:
" D# x7 N. ?, k. I. [4 Y5 |$ sMeasuring the protective earth connection has in fact two reasons. It is to determine impedance
# |& f: v% R) pand cross-sectional area of protective earth connections. For a measuring current of 25 A both
' C0 r" Z0 [* z$ e% O U* ocan be done with one measurement. Requiring a measuring current of more than 25 A it shall be, k* z4 F3 J) I( m0 ?
splitted up into two measurements. In this case, the impedance shall be determined first, using a
- B& z& S" Y) [7 r% X [% Hvoltage not exceeding 6 V.' U9 Y2 A, G* [" D$ W' `/ h) O
If cross-sectional area of the protective earth connections cannot be determined as equal to the- Z. _( L: v+ y; A" D% z# z
one for the phase by measurement of the area, then measurement with current shall be from a) g! J: n9 \3 a7 @. x
source with a higher voltage than 6 V.
- D$ C5 I6 c$ O7 `Explanatory notes:
$ t6 L+ `( T5 L- i+ i9 h7 h8 V( SA circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for# G q# M, |1 h1 @; x* [% L6 k; J
example due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones
7 {0 E; S0 _9 Pbecause of their ability to flash through. In this case, the impedance shall be determined first,
D1 N9 B' ^+ Husing a voltage not exceeding 6 V.: ^' e( M( g2 }* A# ~6 `% o
Using low voltages and low currents has a great impact on the accuracy of the measurement of$ O, x. S9 l8 u4 P4 w4 P. W
low impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated
% R+ V( }8 N' w& ]4 `measuring device.4 Q; i+ Z' C# e6 j& r0 r& J
The relation between rated current of the EQUIPMENT and measuring current is because to
1 U/ m/ }4 P: l# A1 U& gcheck cross-sectional areas of protective earth connections. If parts of the construction or printed( U5 K% S( ~' F/ g# d4 H: g5 m0 I
circuit boards are used for protective earth connections the cross-sectional areas and the ability
0 _# |, c( b7 S: M5 Kof carrying short circuit c urrents are in doubt. |
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