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Decision:
, W2 {9 L4 ]7 L- ], O4 j. l: E8 \Measuring the protective earth connection has in fact two reasons. It is to determine impedance
- \' G, R. L9 B# M# Uand cross-sectional area of protective earth connections. For a measuring current of 25 A both
2 o* F1 n+ T( \, ]# qcan be done with one measurement. Requiring a measuring current of more than 25 A it shall be
4 A2 X& S6 _- \4 Psplitted up into two measurements. In this case, the impedance shall be determined first, using a
8 O3 p0 ~) s9 `2 K R: z3 W& Svoltage not exceeding 6 V.; h- s8 D0 q! V+ d. h) C( D
If cross-sectional area of the protective earth connections cannot be determined as equal to the$ g3 X) x8 P. Q! w+ \
one for the phase by measurement of the area, then measurement with current shall be from a Z* Q! ~4 a+ C1 I+ M
source with a higher voltage than 6 V.7 f3 X! } l& k+ u: c, H6 x
Explanatory notes:% H+ W4 G$ b& B' \1 w
A circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for
' y: Q7 G5 l. i+ _example due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones
& A& ]5 @7 O7 S3 B/ rbecause of their ability to flash through. In this case, the impedance shall be determined first,2 `; Y: \- x9 Y$ [( M7 n
using a voltage not exceeding 6 V.' f5 a/ q. _0 a1 A* R7 ?
Using low voltages and low currents has a great impact on the accuracy of the measurement of1 M' p o/ l+ R% R4 k V
low impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated# n- j! W2 H9 @0 _- |/ H
measuring device.2 G: {- Q8 j! ^' D
The relation between rated current of the EQUIPMENT and measuring current is because to7 \7 {9 X- c; M
check cross-sectional areas of protective earth connections. If parts of the construction or printed# q- R" e2 g( i8 t0 e0 C7 i! k
circuit boards are used for protective earth connections the cross-sectional areas and the ability
" M! ?2 V1 Z5 |7 b! K4 [of carrying short circuit c urrents are in doubt. |
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