Andy and Rich,
The paragraph regarding double fixing for wiring other than power supply
cords is 4.3.9, IEC 950 / UL 1950.
Ed
From: Rich Nute <ri...@sdd.hp.com>
Reply-To: Rich Nute <ri...@sdd.hp.com>
To: andy.v...@mts.com
CC: emc-p...@majordomo.ieee.org
Subject: Re: Double Retention
Date: Tue, 19 Sep 2000 16:08:20 -0700 (PDT)
Hi Andy:
> I have been told that either "double crimp" terminals (fast-ons, ring,
> spade) must be used for insulated wire, or a secondary method must be
used
> to secure the wire's insulation near the point of connection. I have
not
> seen this described in the standards I have read or in the archived
emails
> on the RCIC database - where should I look? At this point, I don't
even
> know if this is a UL or a LVD thing.
This is a long-standing, traditional, and semi-secret
safety requirement. In my experience, it has been
applied by both CSA and UL.
The requirement is based on the concept that safety
must be provided both for normal conditions and in
the event of a fault.
Where a wire could come loose and bridge a safety
insulation, then that wire must have a second
mechanical scheme that prevents the wire from
bridging the insulation.
The requirement is stated in IEC 60950 and its
clones in Sub-clause 3.3.4 for power supply cord
wires. This same requirement MAY be applied to
other wires at hazardous voltage by the many
different certification engineers, each of whom
has a different reason for doing so.
There is a similar requirement for containment of
strands of stranded wire. See Sub-clause 3.3.9.
You didn't ask what are the secondary methods.
Any secondary method that keeps the wire from
bridging a safety insulation is generally
acceptable.
The "double crimp" is acceptable because the
first crimp is to the wire, and the second crimp
is to the insulation. Two, more-or-less
independent fixings.
Best regards,
Rich
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