DSH 595 Requirement for the screws fixing internal parts
http://decisions.iecee.org/icons/ecblank.gif DSH 595
Requirement for the screws fixing internal parts
17.3
60065(ed.6) & 60065(ed.7)
Standard(s):
IEC 60065 : 1998 6th edition
IEC 60065 : 2001 7th edition
Sub clause(s):
17.3
Sheet n.
DSH 595
Subject:
Requirement for the screws fixing
internal parts
Key words:
- Screws
- Fixing internal parts
Decision 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
between the replaced screws and hazardous live parts?
- 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.
- 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.
Decision
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
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
used without any malfunction.
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