DSH 595 Requirement for the screws fixing internal parts

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DSH 595

Requirement for the screws fixing internal parts

17.3

60065(ed.6) & 60065(ed.7) ( m# J5 L) g+ Z' U

; y' ^; ?: f- a+ b9 zStandard(s):
, {  Q: ^; }' I. z5 @! i. HIEC 60065 : 1998 6th edition
IEC 60065 : 2001 7th edition
9 z2 e0 f* h5 W3 E1 O6 K6 u! \Sub clause(s):
; B; ^0 G4 _! V- q6 J3 I17.3
Sheet n.
$ U0 k0 J+ v( A3 f8 kDSH 595
Subject:
Requirement for the screws fixing
2 P6 H" j* o+ J. pinternal parts
- L4 X# W% K& I- h& f6 rKey words:
- Screws
1 k5 z8 `, \) e2 D* f1 ~- Fixing internal parts
Decision approved
during the 44th CTL
meeting 2007
4 `: X6 X: r- p& |  m6 _Question: Should those screws, fixing internal parts, needed to be replaced for a service be captive or
3 r* E* ^; Q* _* z! Pcomply with the insulation distance stated in clause 13 when replaced by screws having the same nominal
  ]0 M. {* u% |! P+ P. M0 X. Xdiameter 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?
! j! }4 M/ _7 s  Q4 C0 |; _6 \6 N- Situation
- 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.
- The screws are inserted from an exterior side or bottom of the amplifier but not fixing the cover of the
amplifier.
( G& k5 A$ t) I' _/ H. s- The screws are not captive but don't comply with the insulation distance stated in clause 13 when replaced by
other screws having the same nominal diameter with a length of 10 times their nominal diameter.
) O- S; y% c  i' GDecision
It's not acceptable. In case of a PCB fixed by just screws without any enclosure, it's acceptable because the
+ c: l! ?* Q+ ~- S1 d  [7 y3 `7 Iservice personnel can make sure that the screws are the right screws during a service. However, in case of the
above 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
! i, I3 X5 h" A) i' k) S. {used without any malfunction.


7 e: |* y4 g6 e9 ]+ `5 ?