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Decision:% A0 \+ b3 O% H
Measuring the protective earth connection has in fact two reasons. It is to determine impedance: c8 Q5 K s0 d5 j. F2 G5 }
and cross-sectional area of protective earth connections. For a measuring current of 25 A both6 b9 N& Z1 l0 @1 Y6 e
can be done with one measurement. Requiring a measuring current of more than 25 A it shall be' [6 Z" P" c* V( l' w4 L" V
splitted up into two measurements. In this case, the impedance shall be determined first, using a
/ X+ v* _3 N- C. M% [+ S4 Xvoltage not exceeding 6 V.
6 b! n" Q ]5 l; q- h0 R8 h7 QIf cross-sectional area of the protective earth connections cannot be determined as equal to the
0 F7 o+ t. u$ _. D' Xone for the phase by measurement of the area, then measurement with current shall be from a) A7 [& Z4 ^5 O/ [, n `) T
source with a higher voltage than 6 V.1 e* [/ P! @; b5 I0 m6 `! _
Explanatory notes:5 f" T- B! l- k4 W+ k5 t
A circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for) v0 v+ L% \. W
example due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones( W2 ?1 x2 i4 a: [
because of their ability to flash through. In this case, the impedance shall be determined first,
) R+ m P8 D9 R+ f; K# Ousing a voltage not exceeding 6 V.
) [3 F0 ^- r+ OUsing low voltages and low currents has a great impact on the accuracy of the measurement of/ a; o" I" s! }1 p3 P6 N# h; ?
low impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated. K" x# u; z7 w6 W* ]+ p
measuring device.
$ w# H J! w5 CThe relation between rated current of the EQUIPMENT and measuring current is because to
1 V$ b w! r7 Q! zcheck cross-sectional areas of protective earth connections. If parts of the construction or printed
& A; \; @5 V/ b5 Fcircuit boards are used for protective earth connections the cross-sectional areas and the ability! R- N# G; e% h, h3 f2 {- K
of carrying short circuit c urrents are in doubt. |
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