DSH 595 Requirement for the screws fixing internal parts

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DSH 595 : x8 O. P8 [8 r. i

Requirement for the screws fixing internal parts ! J* G  ]* R+ @/ c2 o0 {

17.3

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

; J5 C- B* z$ g( ?1 |Standard(s):
( U0 _5 u' {# @: a8 h3 O: _IEC 60065 : 1998 6th edition
IEC 60065 : 2001 7th edition
3 ^* o% ~) M3 T+ J. NSub clause(s):
4 t, ?: W  ?. [, p6 B; B- s17.3
' w  Q/ V; G7 N0 o& N) T5 nSheet n.
4 g1 Q! ^6 Y1 R- L4 m: b! kDSH 595
; O' q( W' }- q& j( t2 GSubject:
Requirement for the screws fixing
internal parts
* Q6 J$ t0 G! qKey words:
3 {6 u9 b' \4 f  L- Screws
5 w' T. @- D* D5 m7 Z% M, b' K- Fixing internal parts
; }# H; ^  g+ A( ~* f) RDecision approved
during 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
diameter with a length of 10 times their nominal diameter? In the latter case, what insulation is required
; M2 t2 l7 Y2 U- v( p7 a  C/ Tbetween the replaced screws and hazardous live parts?
, C" c6 g+ T: s4 r" f! b- Situation
- There is an amplifier which has an internal SMPS board encased by a metal enclosure.
+ n  U! |5 g, Y) ~1 K, k8 j3 J- 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.
- The screws are not captive but don't comply with the insulation distance stated in clause 13 when replaced by
3 j  H2 S: y7 X# B  Kother screws having the same nominal diameter with a length of 10 times their nominal diameter.
# i- @# ~4 @! E6 c+ Z, TDecision
4 h% h4 e8 ]+ O8 I7 J% ?4 gIt'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
" e8 E) a" z; U" K2 \8 D4 P8 eabove 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.
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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