DSH 595 Requirement for the screws fixing internal parts

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DSH 595

Requirement for the screws fixing internal parts $ s/ i* U7 L/ C+ [; R+ M6 u% |5 U

17.3 & D" C' [* g) i- Y

60065(ed.6) & 60065(ed.7) ; d0 b; o1 g2 M9 J8 C, u/ [  `

Standard(s):
; `3 b8 I6 P/ MIEC 60065 : 1998 6th edition
IEC 60065 : 2001 7th edition
Sub clause(s):
, t8 c  l2 f" Z4 ?" ]2 X17.3
Sheet n.
DSH 595
Subject:
1 F2 G5 b+ Q% t2 aRequirement for the screws fixing
internal parts
Key words:
- Screws
- Fixing internal parts
0 o. ]* r6 l- v7 Y  U4 SDecision approved
during the 44th CTL
2 r) M2 V4 m( |' |0 omeeting 2007
6 A/ ~+ x( R$ I& {7 ~4 Z0 ?Question: Should those screws, fixing internal parts, needed to be replaced for a service be captive or
- ~" y1 Q, V$ Y& u3 _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
between the replaced screws and hazardous live parts?
8 {! N( m& |  X2 |9 }  o0 b- r  ?- Situation
0 M1 x3 G) g6 |& Y* i8 r; C- There is an amplifier which has an internal SMPS board encased by a metal enclosure.
. `4 A7 S- W2 x! z, J' x1 n, b- The screws fixing the internal box should be unscrewed to get serviced.
( L" G0 v4 ~8 I$ Y& @- 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
: A- B8 B9 f9 Z% C5 k  X; {$ kother screws having the same nominal diameter with a length of 10 times their nominal diameter.
. m2 R+ U5 Z/ c0 c3 ]3 g8 YDecision
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
& _; j0 g1 H( N/ I3 a+ @. b! 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.
; Q9 B  Z. T  r. D& lIn the above case reinforced insulation is required because after the screws are replaced the amplifier can be
used without any malfunction.
" M2 C# A6 d) P+ E- A8 }
3 D8 @8 ~6 l4 N1 M2 f4 q9 b& y8 M: [