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Decision:
- @$ `1 D& c; j" q2 Z% s# eMeasuring the protective earth connection has in fact two reasons. It is to determine impedance4 k1 u. q& |; y7 ]& ^
and cross-sectional area of protective earth connections. For a measuring current of 25 A both
. O/ ]0 S: r- d0 Q1 l; c/ pcan be done with one measurement. Requiring a measuring current of more than 25 A it shall be
3 F m# i1 l7 h. f# `splitted up into two measurements. In this case, the impedance shall be determined first, using a
. [/ q& K* o9 \ W+ t% Yvoltage not exceeding 6 V.* V( L/ `7 e0 u2 F
If cross-sectional area of the protective earth connections cannot be determined as equal to the
8 G0 ^& i1 V5 w0 yone for the phase by measurement of the area, then measurement with current shall be from a3 z+ W% Y! P3 X) L1 Y6 S
source with a higher voltage than 6 V./ u* U( |& j8 @. V
Explanatory notes:! r" l6 f8 v0 b1 g9 x
A circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for/ D+ }: y* E- _( B! K. z
example due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones
% _, k( j" U4 P( S4 ^because of their ability to flash through. In this case, the impedance shall be determined first,- p* p1 Y4 R3 u8 i& ]0 u( R
using a voltage not exceeding 6 V.) d' G: N( G4 W% h/ u7 {+ {
Using low voltages and low currents has a great impact on the accuracy of the measurement of
6 ?4 ?. S( B/ q/ @7 l) q5 rlow impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated3 B7 x0 | H, V/ C6 q6 @
measuring device.
$ I% h1 f. |1 \ j4 W$ m$ @The relation between rated current of the EQUIPMENT and measuring current is because to
' K& j, C$ ^( \7 y5 e) a& O& v4 ~check cross-sectional areas of protective earth connections. If parts of the construction or printed
) n) E0 f0 l7 z- ncircuit boards are used for protective earth connections the cross-sectional areas and the ability
2 ^! t: a4 g1 R* S& h, ]& xof carrying short circuit c urrents are in doubt. |
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