DSH 595 Requirement for the screws fixing internal parts

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DSH 595

Requirement for the screws fixing internal parts

17.3 ) p- r2 f2 t  K" Z. W' N

60065(ed.6) & 60065(ed.7)

5 K; c4 b. _8 {Standard(s):
IEC 60065 : 1998 6th edition
IEC 60065 : 2001 7th edition
Sub clause(s):
  X5 x- B% ~3 m3 a5 l) l/ S* O17.3
# R4 j& h: s/ V, ]) W. k, I7 J5 nSheet n.
" q( D( J0 v) `DSH 595
Subject:
3 X1 j4 c  z" T' [& ORequirement for the screws fixing
: B/ R! C9 \9 ]internal parts
Key words:
2 e" j8 X- X: W% j9 I- Screws
: R& u9 ^. m+ I/ U3 l1 E# ^: c+ n, l- Fixing internal parts
8 b  L1 M, W( R& t2 fDecision approved
8 e3 `5 O4 Z5 g5 l+ sduring the 44th CTL
meeting 2007
Question: 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
- C7 A3 @' ^, Y3 X2 r+ wdiameter with a length of 10 times their nominal diameter? In the latter case, what insulation is required
- c* E! x0 T; H: Wbetween the replaced screws and hazardous live parts?
  Z8 }% D/ q7 ?. ?7 ^- F- Situation
  u. |: I9 k9 F- v- There is an amplifier which has an internal SMPS board encased by a metal enclosure.
- The screws fixing the internal box should be unscrewed to get serviced.
* w0 w+ k! Q6 W5 j; R- The screws are inserted from an exterior side or bottom of the amplifier but not fixing the cover of the
2 Z2 m1 \0 K4 D0 H) }( [* K9 Oamplifier.
- The screws are not captive but don't comply with the insulation distance stated in clause 13 when replaced by
3 m% v" e3 H7 s" |+ v# |; x6 Zother screws having the same nominal diameter with a length of 10 times their nominal diameter.
6 ~9 b' H8 ^3 p' UDecision
It's not acceptable. In case of a PCB fixed by just screws without any enclosure, it's acceptable because the
7 J$ F+ ~! k' ^9 n5 Eservice personnel can make sure that the screws are the right screws during a service. However, in case of the
1 A* M$ o) c: {3 L+ gabove SMPS board encased by a metal enclosure, it's not acceptable because the service personnel can't know
whether the screws are the right screws or not during a service due to the internal metal enclosure.
3 g3 B& J0 E$ X: }0 l. l! U8 U9 x* RIn the above case reinforced insulation is required because after the screws are replaced the amplifier can be
" X" ~( P$ l7 f; V  P1 Sused without any malfunction.
: r3 j) d3 G+ o7 v1 y; D
7 k! _- o$ C; `& J