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Decision:! v, n) S8 U; Y( R6 f* B) t( ~
Measuring the protective earth connection has in fact two reasons. It is to determine impedance
, g% _/ C( m1 F7 t* ]/ K4 tand cross-sectional area of protective earth connections. For a measuring current of 25 A both+ }! x0 n. g, t( Z% B9 I# Z
can be done with one measurement. Requiring a measuring current of more than 25 A it shall be
% |! W3 J* g; |6 W! N/ P# n- Osplitted up into two measurements. In this case, the impedance shall be determined first, using a
. k) A6 N* A4 x! D1 l6 Avoltage not exceeding 6 V.! ^6 G/ b0 C& k( d5 g: J
If cross-sectional area of the protective earth connections cannot be determined as equal to the
' f0 q$ B4 w# H( P6 Gone for the phase by measurement of the area, then measurement with current shall be from a: H. i5 {) O- T( X5 A/ I4 o
source with a higher voltage than 6 V.. n) i4 s8 K5 k5 [+ d2 K, r0 R
Explanatory notes:% }- I2 g. q+ h. Q# }$ u( _6 v
A circuit to the PROTECTIVE EARTH TERMINAL may have zones of higher impedance, for
5 W& ~* O3 {# j* cexample due to oxidation of materials. Voltages higher than 6 V prevent detection of such zones- b- K3 ^- g; J
because of their ability to flash through. In this case, the impedance shall be determined first,
8 ~, L" \) ?% d: Q& Musing a voltage not exceeding 6 V.
! \0 ?% Z+ u6 R( kUsing low voltages and low currents has a great impact on the accuracy of the measurement of$ l' x0 \! t5 }* [7 B, U; }
low impedances. Impedances in the range of 0.1 W and 0.2 W then require a sophisticated
# ~( Z" E: X; D9 w/ v6 z) B _" Tmeasuring device.
# d! v" n7 q8 f5 WThe relation between rated current of the EQUIPMENT and measuring current is because to
5 p* F0 W8 Y' \7 i7 Zcheck cross-sectional areas of protective earth connections. If parts of the construction or printed
, }: g9 L. S5 c4 d7 r: O6 acircuit boards are used for protective earth connections the cross-sectional areas and the ability3 d. \; r3 x5 m9 m: v) a$ w J
of carrying short circuit c urrents are in doubt. |
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