I think the contrary...
The diode is there to blow the fuse. Why use a diode across the
terminals and not in series ? The 0.7V voltage drop across the series
diode might be too much (especially in 12V devices), when connecting a
diode in shunt this problem is omitted. The consequence is that you blow
the fuse when you connect the power wrong.

Hoping this is my first valuable contribution to the piclist... oops OT

Greetings
Kurt Herremans


Mark Devin Newland wrote:
>
> Although it may be true that this will work, I don't think
> that is the reason WHY they put it there.  Typically,
> a manufacturer will put a reverse biased diode across
> the power supply terminals as a form of transient
> protection.  If a voltage spike appears on the positive
> terminal greater than the reverse breakdown voltage
> of the diode, the diode will bleed the excess to ground.
> It may not be as good as a 79 cent transorb but for 7
> cents the diode is ALOT better than nothing.
>
> Mike DeMetz wrote:
>
> > > Provide the simplest protection against accidental
> > >     reverse connection (a series diode), mark the
> > >     terminals clearly '+' and '-', color the terminals
> > >     red and black respectively, and the intended User
> > >     will understand what's required.
> > >
> > Another method I've seen on CBs is to connect a diode across the power
> > terminals reversed biased. Connecting backwards blows the fuse.