Joe,
If you use Amendment 4 of IEC 950, and fall into the TNV-1 category, you can
use operational insulation and a dielectric test between SELV and TNV. Of
course amendment 4 is not universally accepted (i.e. Australia), but UL will
allow the TNV 1 conditions when evaluating to UL-1950 3rd Edition.
Jim
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From: treg-approval
To: treg
Subject: IEC 950 / UL 1950 creepage and clearance requirements
List-Post: treg@world.std.com
Date: Thursday, May 08, 1997 3:01PM
To any and all safety gurus,
I am in the midst of trying to minimize the creepage and clearance
requirements between TNV and SELV called out in IEC 950. My
interpretation of tables 5 and 6 in sections 2.9.2. and 2.9.3 are that
minimum clearance is 2.0mm and minimum creepage is 2.5mm. This is
based on a global design using up to 250V mains, pollution degree 1 &
2 and Material Group IIIa + IIIb. The application is for Class I as
well as Class II systems.
I could not find a reference explaining the definition of the
Material Groups and would appreciate any insight into a clause, etc.
which I could reference to reduce these spacing requirements. Please
also advise if you are in need of further details.
Thx,
Joe
**********************************************************************
Joe Finlayson
Manager, Compliance Engineering
Microcom, Inc.
