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Decision:
! u) W) v4 }# i% JMeasuring the protective earth connection has in fact two reasons. It is to determine impedance9 E% n' y. g/ A5 c; [% J4 z' V
and cross-sectional area of protective earth connections. For a measuring current of 25 A both0 Y3 s, n' Y% v
can be done with one measurement. Requiring a measuring current of more than 25 A it shall be
* A0 ~9 q- ]+ ^; V; }splitted up into two measurements. In this case, the impedance shall be determined first, using a/ A& J: B2 f' ]# y* @
voltage not exceeding 6 V.
( X% ]) i, G! eIf cross-sectional area of the protective earth connections cannot be determined as equal to the9 V. F7 S: N( Q
one for the phase by measurement of the area, then measurement with current shall be from a7 _0 }% J; Y. p1 l" G6 w
source with a higher voltage than 6 V.
4 C9 t; H" @6 iExplanatory notes:
" B* F8 d& D4 B3 Y6 @A circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for
2 D( O! ~/ \+ {" D% @0 Rexample due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones1 ^* _+ u- a4 @ G$ Y4 H
because of their ability to flash through. In this case, the impedance shall be determined first,
" H0 i, U8 h2 e! z3 Lusing a voltage not exceeding 6 V.
0 O. W1 W1 j) G/ T7 l& f: x5 xUsing low voltages and low currents has a great impact on the accuracy of the measurement of( n) J2 w% f' P, `; q
low impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated$ d6 w' J# t4 ]6 P: a
measuring device.3 k( g& N4 o# J i5 P3 D v/ h
The relation between rated current of the EQUIPMENT and measuring current is because to; Z. r. n- x) ]: a% ~) W
check cross-sectional areas of protective earth connections. If parts of the construction or printed0 K K, z! Z, E; @! ^* s
circuit boards are used for protective earth connections the cross-sectional areas and the ability
# m9 L4 {9 P/ e- ]of carrying short circuit c urrents are in doubt. |
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