Re: PCB Design

["David Buckley" <db@xxxxxxx>]

--- In ukha_d@xxxxxxx, Stuart Poulton <stuart.poulton@a...>
wrote:
> Hi All,
>
> Does anyone know how to calculate the track width required to carry
mains voltage
> of a specific current on a PCB ?

In short - this is a grey area.  There is a set of data widely quoted
(IPC) but it is old, was determined by experiment (ie it has no basis
in theoretical science) and many folks frankly dont believe it.  Have
a google search, theres lots of wingeing.  I liked this item, from
someone who should know what he's on about:

http://groups.google.com/groups?hl=en&lr=lang_en&ie=UTF-
8&safe=off&selm=35DBC278.52BFA1D7%40appliedcad.com

If you are shoving lots of power around on a PCB, in addition to wide
traces (or indeed changing of PCB material to increase thickness of
track, use 3oz rather than 1oz) you can use PCB busbars (RS 435715),
or augment the trace with single core wire soldered onto the trace
all the way along to make it a "thick" trace.  This is often done
on
mains light dimmers; 4 x 10A needs a lot of current carrying
capability.

The reason for all this palava is, of course, to limit temperature
rise.  ISTR that 10C rise of temperature halves the life of a piece
of kit.

Oh yes, there is one other thing.  Get a short across the load, and
your track width or fusing wrong, and the PCB trace vaporises.
Whilst not as loud as an electrolytic cap letting go, it is
adequately loud and scary, and you _will_ jump some distance :-))

David.