If your equipment is being approved to UL-1950 "Information Technology 
     Equipment", then you want to look up "CLEARANCES" and "CREEPAGE" 
     distances.
     
     This is also covered in the European Product Safety Standard EN-60950. 
     Both UL1950 and EN60950 are national interpretations of the 
     International Standard IEC-950.
     
     You need to know the following before calculating separation of 
     circuits:
     
     1.   CTI Rating of your board
     
     2.   Working voltage of the trace:
     
          Peak value for non-sinusoidal,
          RMS value for sinusoidal,
          DC level DC voltages.
     
     3.   Pollution level of the environment where the equipment is being
          used.
     
     4.   Insulation category that you need: Basic, Operational,
          Reinforced.
     
     Then, you can start reading the charts for separation distances.
     
     Doug McKean
     ADC Video Systems
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: RE: UL Approval
Author:  [log in to unmask] at internet-mail
Date:    4/10/96 3:09 AM


Kitty Hines just posted the following. I sent her a reply, but I think it 
went directly to her mail, not over the designercouncil. So I am posting it 
to the council for info. If this turns out to be a dual post, I apologize!!
     
     
At 10:16 PM 4/8/96, you wrote:
>I am looking for information on the spacing requirements necessary 
>to meet UL approval.  Can anyone give me a reference on where to 
>find these specs?
>
>Thanx for your help.
     
     
Two years ago I had the same problem. I talked with a very helpful guy named 
Michael Cusanelli at UL Labs in Santa Clara. He was at 408-985-2400 ext 2997 
--- don't have a clue if he still is.
     
The relevant spec is UL 1950 (US) or IEC 950 (Common Market), parts of which 
are still voluntary until the year 2000.
     
If the working voltage is under 50 v (dc) or 71 v P-P, there is no spec 
(Section 2.9.4) If the working voltage exceeds that, then there are specs 
for separation, but not on trace thickness or width. There are two tables in 
Section 2.9.5 that apply --- Table 7 IF the traces are conformally coated, 
Table 5 if they are not.
     
When I called them asking for this information, they faxed me the relevant 
pages. Probably would do the same for you if you called them.
     
Doug Brooks, President
UltraCAD Design, Inc.