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Decision:3 j( k/ @9 ^6 H! t$ I1 Z- A6 @9 }
Measuring the protective earth connection has in fact two reasons. It is to determine impedance* y. C* Q$ {1 e) K& Q; |5 X. N
and cross-sectional area of protective earth connections. For a measuring current of 25 A both1 E( Z( S7 j, a* \* j4 x" L; I* b
can be done with one measurement. Requiring a measuring current of more than 25 A it shall be
6 `5 k8 \& u, j/ F/ \( Q0 W/ ysplitted up into two measurements. In this case, the impedance shall be determined first, using a
& o5 Q5 u7 t5 b i) Q/ K8 p2 ]voltage not exceeding 6 V.
5 n% x1 V( B* CIf cross-sectional area of the protective earth connections cannot be determined as equal to the
% f. Y, O" D" Z S T1 U* `/ X/ Tone for the phase by measurement of the area, then measurement with current shall be from a+ A6 A. S) `+ q, D
source with a higher voltage than 6 V.
L, ~- Z" z0 dExplanatory notes:+ m7 o3 k* H3 L! u; P% a$ T! W
A circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for
0 w% K4 W- ~; yexample due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones$ M! K5 X% \- m8 y* E- U
because of their ability to flash through. In this case, the impedance shall be determined first,
$ D: K* j3 g+ x4 W! `: y% l3 l3 Qusing a voltage not exceeding 6 V.1 [! t7 K) A3 B
Using low voltages and low currents has a great impact on the accuracy of the measurement of8 X) N1 y* i1 M w) W) @
low impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated
- W# t2 x3 f6 G! C; [- e6 _8 t4 `& kmeasuring device.
2 |9 @1 H H5 ?$ @The relation between rated current of the EQUIPMENT and measuring current is because to6 @& f/ E& E) X, [! u$ D1 `$ {
check cross-sectional areas of protective earth connections. If parts of the construction or printed' O$ A+ h( M5 ]- W
circuit boards are used for protective earth connections the cross-sectional areas and the ability# F) `" ?2 S( ^ D
of carrying short circuit c urrents are in doubt. |
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