Isaac Marino Bavaresco wrote:
> There is an IEC norm that deals with this. If I recall it correctly, the
> tracks must be kept away 8mm for 220V and 4mm for 110V before the
> current passes some sort of current-limiting or protection device.

The power input is pretty well protected -- there's a 10A fuse built in 
to the IEC socket, and a 500mA fuse on the primary side of the power 
supply transformer.

> I think you may need 8mm or more between mains tracks. The distance from
> mains to low voltage tracks may be even larger.

I've (finally) found the section on PCB design in AoE -- page 841 in the 
Second Edition. 10A in a 0.170" wide track on FR4 board with 2oz copper 
will cause a 10C temperature rise. The same current in a 0.080" wide 
track will cause a 30C temperature rise. According to the text, "for 
other copper thicknesses, just scale the widths accordingly." So double 
the numbers then (10C rise, 10A, 1oz = 0.340").

For half an amp the numbers are a little more reasonable.. 0.008" for a 
10C rise. That's less than my standard track size (15 mil).

For high-voltage stuff:
   PC runs with high voltage need correspondingly wider spacing -- a 
good rule is 5 volts per mil (0.001").

So the 100mil (2.54mm) figure is probably about right. The off-board 
connectors I'm using (5.08mm pitch PCB mount terminal blocks) are rated 
to 600V, which seems to add further value to the track-to-track spacings 
I've found. The solder pins are, however, rather thin. Thin enough to 
make me wonder if the manufacturer is bluffing about the 10A current rating.

> Get a copy of the graphical table calculator (I don't know how it is
> called in English :). Board manufacturers can give you some.
> 
>> The PCB blanks I'm using are 1oz single-sided, FR4 laminate. If anyone 
>>   
> 
> So you track thickness is already known and fixed.

.. But I can always increase it if necessary -- PC power supplies often 
have thick layers of solder applied to certain tracks on the PCBs 
(usually in the mains and HV-DC sections) to boost the power handling 
capacity of said tracks.

It's a hack, but if it works for the PCB manufacturers.. why not?

-- 
Phil.
piclist@philpem.me.uk
http://www.philpem.me.uk/
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