The issue is not so much about what the relative reliability is. The
issue is that if the DPDT switch fails you may not be able to connect to
either source of electrons. If one of the SPST switches fails, you
always have the other one.
Dick Tasker
messydeer wrote:
>
> Thanks, E., for bringing up the issue of single point of failure. Hadn't thought
about that, which makes me ask some questions about DPDT vs SPST switches.
>
> Looking at the schematic of a DPDT switch it looks like there are two circuits,
an upper and a lower. Their terminals are separate but contained in the same
housing. They also use the same lever and the mechanism the lever connects
to that makes and brakes the contacts.
>
> If the only way a switch failed was through these shared components, then a DPDT
would have the same reliability as a SPST, so there would be a single point
of failure.
>
> And if DPDT's never failed at these shared components, then having one DPDT would
be just as reliable as having two SPST's, and there wouldn't be a single
point of failure.
>
> I'm sure the truth lies somewhere between these two extremes. If it turns out
that a DPDT has 90% of the reliabilty as two SPST's, I might stick with just
one DPDT. If it has only 20% of the reliabilty of two SPST's, I might consider
going with two switches.
>
> --------
> Dan
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=273392#273392
>
>
>
