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) 8 w6 o# {5 [4 i  n. v- X4 G% }# @

6 E) U3 h: ~. l6 q5 W2 \) NStandard(s):
IEC 60065 : 1998 6th edition
IEC 60065 : 2001 7th edition
Sub clause(s):
; K3 [8 H, ?) ]3 K& i* P17.3
3 a* ]- ~8 C3 l& x! r" PSheet n.
9 s: H- ]" R2 m4 a& QDSH 595
Subject:
Requirement for the screws fixing
1 i* N6 ~' J- r" ]! O; f) V! pinternal parts
Key words:
- Screws
% D8 O. w2 H$ D8 J3 g9 R& D- Fixing internal parts
Decision approved
during the 44th CTL
( m4 p4 p' _+ o5 m/ _5 }3 y& Jmeeting 2007
Question: Should those screws, fixing internal parts, needed to be replaced for a service be captive or
9 e* H0 l( {: U* Q9 K0 s9 Scomply 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
between the replaced screws and hazardous live parts?
, o- B8 N+ C% {, G4 f# K/ A& ]- Situation
) k; \- _8 J0 j! r7 S0 N- There is an amplifier which has an internal SMPS board encased by a metal enclosure.
3 M4 \8 X% L+ ]/ k9 W; d# ?- The screws fixing the internal box should be unscrewed to get serviced.
, w4 |; \* H; ?$ I& G$ t- 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
( r9 R) J& a, D8 B  `6 J* mother screws having the same nominal diameter with a length of 10 times their nominal diameter.
Decision
It's not acceptable. In case of a PCB fixed by just screws without any enclosure, it's acceptable because the
* l% O9 f7 V8 ]$ T# L9 I: [service personnel can make sure that the screws are the right screws during a service. However, in case of the
( J. W# \( f1 U+ K" m+ labove SMPS board encased by a metal enclosure, it's not acceptable because the service personnel can't know
( C* _5 J; [8 f, C! w# {- Twhether the screws are the right screws or not during a service due to the internal metal enclosure.
, ?. o  U4 c4 E3 r! S5 b' y3 l& ?In the above case reinforced insulation is required because after the screws are replaced the amplifier can be
, m( W! k) Z* yused without any malfunction.
% G2 @" o8 s: z0 _; B: Y$ }

) b0 t, \& N3 `: O) L3 o