DSH 595 Requirement for the screws fixing internal parts

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DSH 595   n* F: Y* z7 P. c$ c+ m! R

Requirement for the screws fixing internal parts

17.3

60065(ed.6) & 60065(ed.7) - A9 `' K& \, b5 N& c( f' ~

6 E) N8 t4 ?# g0 k4 }Standard(s):
: [6 c# }6 g2 ]3 V% h, X2 ?IEC 60065 : 1998 6th edition
! v& B, Q5 I6 d9 k7 UIEC 60065 : 2001 7th edition
& ~! K) J5 s6 ]' z' W) ^$ N$ B! ~Sub clause(s):
: r  T, F% ~: F, Z, O17.3
& W" l% t) n/ h, B) pSheet n.
DSH 595
$ E4 }- L' D: L# FSubject:
Requirement for the screws fixing
internal parts
: Z# y. j, w  @4 H2 y: BKey words:
( h  C: R: K8 d# u4 b- Screws
. S: I$ I; D4 i4 O1 D* @- Fixing internal parts
Decision approved
during the 44th CTL
meeting 2007
  i/ |8 H$ e7 n( U( OQuestion: Should those screws, fixing internal parts, needed to be replaced for a service be captive or
comply with the insulation distance stated in clause 13 when replaced by screws having the same nominal
, q$ t" I/ L% {; D* x5 @diameter with a length of 10 times their nominal diameter? In the latter case, what insulation is required
between the replaced screws and hazardous live parts?
3 j5 e! w: \" X0 j+ \' t# q, c- Situation
5 B9 v. }  T$ L! y- There is an amplifier which has an internal SMPS board encased by a metal enclosure.
7 k  o" T5 Z* ~  n; m- The screws fixing the internal box should be unscrewed to get serviced.
- The screws are inserted from an exterior side or bottom of the amplifier but not fixing the cover of the
amplifier.
" M6 c; D  p7 C- The screws are not captive but don't comply with the insulation distance stated in clause 13 when replaced by
' d9 J0 Y: t8 {. `- M3 q, Dother screws having the same nominal diameter with a length of 10 times their nominal diameter.
- h2 e) t  h& m) E/ h" R! ^Decision
It's not acceptable. In case of a PCB fixed by just screws without any enclosure, it's acceptable because the
service personnel can make sure that the screws are the right screws during a service. However, in case of the
9 ]0 b" j3 T& N. x/ aabove SMPS board encased by a metal enclosure, it's not acceptable because the service personnel can't know
) d) f  y2 V% j4 F$ z, Cwhether the screws are the right screws or not during a service due to the internal metal enclosure.
In the above case reinforced insulation is required because after the screws are replaced the amplifier can be
used without any malfunction.

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