At 09:20 AM 7/4/01 -0400, Jeff Jolie wrote:
>Hi All,
>Can someone point me to where I can find information on trace width and
>trace to trace spacing to comply with UL and CE requirements. I have 3
>phases and neutral I need to route (120VAC/2A or 220VAC/1A). I've been told
>the requirements are different for phase to phase vs phase to neutral trace
>spacing. Thanks for the help.
http://www.ul.com/info/standard.htm
UL sells its standards through COMM 2000, you can find a link to them on
the above page.
The UL standards I have seen are targeted at specific products, generally;
perhaps one exists now, but I have not seen a generic "printed circuit
board" standard from them. I advise getting the standard for the specific
product, it is much more complicated than simple spacing requirements.
Nevertheless, I happen to have an old Television Receivers and Video
Products standard, and this is from it:
***
16.3 Function insulation is the insulation necessary for the proper
functioning of the appliance and for basic protection against electric
shock and the part is to have
A. A dielectric voltage withstand capability of 1000 volts for 1 minute and
B. Minimum acceptable through-air or over-surface spacings of 1/16 inch
(1.6 mmm) in circuits of 125 volts or less.
***
Supplementary insulation is required for parts which are not grounded and
which are accessible and that might become a shock hazard due to a
component failure, or a reduction in spacings as a result of user servicing
and handling, and:
***
16.4 ... The minimum spacing through supplementary insulation is to be no
less than that required for the same material employed as functional
insulation. The minimum spacing through supplementary insultation used in
circuits involving 125 volts or less is to be 1/32 inch (0.8 mm) and this
insulation is to have a dielectric voltage withstand capability of at least
2500 volts for 1 minumte. The minimum acceptable through-air or over
surface spacings between conductive parts separated by supplementary
insulation are to be 1/16 inch (1.6 mm).
***
However, this is not right on point. UL standards seem to focus on results;
to be certified, they will not be so much interested in exact spacings on a
circuit board as what happens when they stick a hipot on it with 1000 to
2500 volts. They will also examine the physical layout of things for shock
or fire hazards.
Note that the IPC standards for spacing vs. voltage are highly
conservative. I've done some actual testing and actual breakdown occurred,
as I recall, somewhere around ten times the voltage indicated in the
standard at a certain spacing. But that was a long time ago; verify this
information before betting the product on it. Basically, if you follow IPC
standards and you use a solder mask, your board is unlikely to fail. Use
the standards for 220V. Use extra spacing if a breakdown would result in a
shock hazard.
But there is, in the standard I have, a Spacing section:
***
8. Spacings
Mechanical
8.1 A spacing of 1/8 inch (3.2 mm) minimum over surface or through air
shall be maintained between uninsulated live parts of the primary or supply
circuit and both of the following parts:
A. Live parts of the opposite polarity.
B. Accessible metal parts.
Exception: The spacing requirements in paragraph 8.1 do not apply
where the location and relative arrangement of parts are such that adequate
permanent separation is assured.
***
Bottom line: if you can maintain a spacing of 1/8 inch, do it, it is
guaranteed acceptable unless proven otherwise. If that spacing is not
possible, then any spacing which can be known to be permanently adequate
can be used. 1/8 inch is a safe harbor.
If there is an 0.156 inch spacing Molex power connector on the board, with
60 mil holes in the footprint, and a 15 mil annular ring on the holes,
which is about the minimum I'd consider acceptable for something like that,
I'd rather have more, the pads will be 90 mils in diameter and the spacing
will thus be 66 mils, about half of the 125 mil spacing. If you skip pins
(have a dead pin in between), the accumulated spacing will be 132 mils,
which is within the safe harbor. But, as I recall, I've seen such
connectors with at least 125 V AC between adjacent pins, on designs
intended for UL approval and, to my knowledge, they passed.
As to trace widths, they must be sufficient so as not to present a fire
hazard, and the temperature rise in the track must be limited to that which
can be withstood for the board material or anything else in contact with
it. If you design for 20 degree rise maximum under standard operating
conditions, and 60 degree maximum rise under fault conditions -- unless the
normal interior temperature of the system goes above 45 degrees C. --, it
should be adequate. For 2 amps and 2 ounce copper, this would be about 12
mils, and fault current could be 4 amps. Don't use a trace that small for
power! I'd use 50 mils minimum, which would allow 6 amps, 10 amps fault.
The power should be fused such that fault current cannot long exceed the
continuous rating of the track.
Perhaps someone has more extensive or more recent experience with UL, or
can enlighten us as to CE requirements.
[EMAIL PROTECTED]
Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433
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