Just a couple of points from another viewpoint:

In my experience, the voltage drop (the product of current and resistance) through the conductor
becomes a limiting factor before the temperature rise above ambient.  IMO both factors should be
evaluated.  The IR (voltage) drop can be estimated several ways including taking measurements
from an existing design.

The other point concerns the regulatory agencies when dealing with higher voltage circuits.  UL
has standards that deal with the application of the finished product.  The particulars regarding
separation of high voltage circuits will vary somewhat with the standard.  For example the
requirements for medical devices are different than those for office equipment.  The governing
regulatory agencies should be contacted for guidance on this issue before committing the minimum
spacing on a board design.

Don Vischulis

Ralph Hersey wrote:

> W D Stewart wrote:
> >
> > I'm looking for design information on the width and thickness of
> > traces for a printed circuit board I am trying to design.  It will be
> > carrying 220VAC at 8, 5, 2, and 1 amps and 120VAC at 4 and 1 amps.  Is
> > there any general reference guide that gives 'rule-of-thumb'
> > guidelines re this?
> >
>
> The conductor's cross-sectional area requirements can be obtained from
> IPC-D-275, Table 3-4, or IPC-2221, Table 6-4.  Or better yet, visit the
> website of UltraCAD Design Inc, <http:\\ultracad.com>, Doug Brooks has
> done an excellent job in developing and making available a model for
> calculating the conductor cross-sectional area requirements for limiting
> the thermal rise above ambient.  These models will replicate the above
> referenced IPC charts and have been extended (by some addition
> referenced technical papers) or get ahold of the latest copy of Printed
> Circuits Design magazine, his technical paper and model is in his
> column.
>
> The other concern you've got is voltage, simply stated, you can use the
> IPC design conductor spacing tables ---- but I suspect for the above
> application they may not be suitable.  This is because the voltage 220 &
> 120 Vac are electrical "primary power", and are subject to regulatory
> requirements (UL, CSA, VDE, IEC, etc) and they have different conductor
> spacing requirements for "exposed" conductor spacing.  In the USA, 220
> and 120 Vac are the same voltage with respect to neutral and ground (120
> Vac).  As I recall, for USA the requirement was 1.5 kV + twice the
> applied voltage (1.5 + 2 * 120) or 1750 Vac test voltage and spacing.
> If you want/need, I can dig in my files and come up with the spec.
> requirements.  I seem to recall the Eurpoean requirements were like
> about 2.5 kV.
>
> Hope this helps, if you need more info. (if other technetters don't
> respond with addition a info.) drop me an e-mail
>
> Ralph Hersey
>
> Ralph Hersey & Associates
> 3885 Mills Way
> Livermore, CA 94550-3319
> PHN/FAX: 925.454.9805
> e-mail: [log in to unmask]
> snip the rest  -------------------------------------------------

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