DSH 168A Resistance to corrosion of current-carrying parts

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DSH 168A " \! Z6 w# q& P0 i' o% T9 j

Resistance to corrosion of current-carrying parts

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Generality

- X" _# C2 h, K9 cQuestion:
: S. j1 s% \( V( O2 d" c+ VHow to judge whether a current-carrying part is resistant to corrosion ?
1 l7 b- s" n1 V7 m2 _5 ]$ q" m" O! PDecision:
CEE Recommendation n. 9 “Corrosion of current-carrying parts” may be applied to judge whether a current-carrying part is resistant to corrosion .
It is quoted in CB Bulletin No. 41 (September 1981).
& N1 u8 r: J5 h- yIn the following, for convenience, is reported a part of it:
  I5 w* }7 p5 v$ t# `/ fRECOMMENDED TEXT, SCREWS, CURRENT-CARRYING PARTS AND CONNECTIONS.
% ?/ ^: n4 x5 ]% g9 ca) Current-carrying parts and parts of terminals shall be of a metal having, under the conditions occurring in the equipment, adequate mechanical strength and resistance to corrosion.
Compliance is checked by inspection and, if necessary, by measurement and by chemical analysis.
After all the tests of the relevant specification, the current-carrying parts and parts of terminals shall show no appreciable deformation.
# R& Q# C7 y) b! I% N! y& YExamples of suitable metals, when used within the permissible temperature range and under normal conditions of chemical pollution, are:
- copper,
: B5 S9 V9 V; W' y# x- an alloy containing at least 58% copper for parts that are worked cold or at least 50% copper for other parts,
; u3 B8 z9 M8 L" X+ w- stainless steel containing at least 13% chromium and not more than 0,09% carbon,
- steel provided with an electroplated coating of zinc according to ISO Publication 2081-1973, the coating having a thickness of at least:
7 y8 a; x/ q  x4 G$ G2 d4 h) A* 5 T ISO grade “1 mild” for ordinary equipment,
* 12 T ISO grade “2 moderate” for jet-proof and splash-proof equipment,
  j' \- R6 v$ H7 I7 \* 25 T ISO grade “3 severe” for jet-proof and watertight equipment.
- steel provided with an electroplated coating of nickel plus chromium according to ISO Publication 1456-1974, the coating having a thickness at least equal to that specified for:
* service condition no. 2 for ordinary equipment,
2 O6 v% H' t9 ?" p! f* service condition no. 3 for drip-proof and splash-proof equipment,
! y6 T! A9 X1 \: W$ l* X* service condition no. 4 for jet-proof and watertight equipment.
& S) v0 j% k5 y# M9 N! C- Aluminium and its alloys, provided special measures are taken for removing, where necessary, the oxide layer, for obtaining a sufficient and durable contact pressure and for ensuring that the point of connection withstands the corrosion test specified;
however, until a suitable corrosion test and an electrical performance test are available, aluminium and its alloys should preferably not be used for current-carrying parts and terminals within the equipment.
Zinc and other metals which are soft or liable to creep are not considered to be suitable for current-carrying parts and terminals .
2 V& p( P+ @, H2 }( F! JThe thickness of the electroplated coatings on steel may be determined by the magnetic method described in ISO Publication 2178-1972, or by microscopical
measurement described in ISO Publication 1463-1973.
b) Under moist conditions, metals showing a great difference of electrochemical potential with respect to each other shall not be used in contact with each other .
Compliance is checked by inspection.