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Decision:3 p) k! M. d1 E$ {& I9 X' @
Measuring the protective earth connection has in fact two reasons. It is to determine impedance
* t4 I7 t% z- S6 L5 p# wand cross-sectional area of protective earth connections. For a measuring current of 25 A both
- T( g" [, K$ d) x7 Y2 a' v$ ~3 q0 ccan be done with one measurement. Requiring a measuring current of more than 25 A it shall be
$ _7 i" w- n5 y# S' b4 asplitted up into two measurements. In this case, the impedance shall be determined first, using a
3 i" \0 s% n4 {5 l2 c1 Pvoltage not exceeding 6 V.
4 R5 R: E: \4 U v1 ]! cIf cross-sectional area of the protective earth connections cannot be determined as equal to the
|! e" b, W6 S2 [3 h+ X; E$ ^5 tone for the phase by measurement of the area, then measurement with current shall be from a
$ t1 X' p/ {. D, u4 E( wsource with a higher voltage than 6 V.
8 \/ H& g& J! v$ Q/ f' `0 uExplanatory notes:
`2 j. d- ]' Q( u8 {' u+ bA circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for
4 M, v" {. g, N! u: U" uexample due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones& [% h3 l; W# r, k% o$ r
because of their ability to flash through. In this case, the impedance shall be determined first,
o5 W( Y2 l8 y' uusing a voltage not exceeding 6 V.
' R, u/ \. w; l( F% s2 nUsing low voltages and low currents has a great impact on the accuracy of the measurement of3 X# o/ D& i: D2 r0 t' c/ y
low impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated! @% a! {1 C+ ^# G
measuring device.
' j% t5 g; o8 I3 hThe relation between rated current of the EQUIPMENT and measuring current is because to
2 ?, i2 l7 l, I! k5 Q8 j8 [+ {check cross-sectional areas of protective earth connections. If parts of the construction or printed# C! b: U: R& Y$ W
circuit boards are used for protective earth connections the cross-sectional areas and the ability6 @/ x- L. G, X
of carrying short circuit c urrents are in doubt. |
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